431 lines
28 KiB
Markdown
431 lines
28 KiB
Markdown
---
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layout: page
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title: EPI
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---
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Legend
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======
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- Solved
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- Attempted
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- Needs Revisit
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Solutions
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=========
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Primitive Types
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---------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Computing the parity of a word | a | b | c | d
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| Swap bits | | |
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| Reverse bits | | |
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| Find a closest integer with the same weight | | |
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| Compute *x × y* without arithmetical operators | | |
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| Compute *x/y* | | |
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| Compute *x^y* | | |
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| Reverse digits | | |
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| Check if a decimal integer is a palindrome | | |
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| Generate uniform random numbers | | |
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| Rectangle intersection | | |
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Arrays
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------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| The Dutch national flag problem | | |
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| Increment an arbitrary-precision integer | | |
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| Multiply two arbitrary-precision integers | | |
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| Advancing through an array | | |
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| Delete a key from an array | | |
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| Delete duplicates from a sorted array | | |
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| Buy and sell a stock once | | |
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| Buy and sell a stock twice | | |
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| Enumerate all primes to *n* | | |
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| Permute the elements of an array | | |
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| Compute the next permutation | | |
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| Sample offline data | | |
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| Sample online data | | |
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| Compute a random permutation | | |
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| Compute a random subset | | |
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| Generate nonuniform random numbers | | |
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| The Sudoku checker problem | Solved | 3-4 hrs | n/a | apr 29 | Spent 1 hr just on row and col check, looked up box validation
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| Compute the spiral ordering of a 2D array | Attempted | n/a | solve by simulation |
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| Rotate a 2D array | Solved | 2hrs | transpose and flip horizontally | apr 29 | fav problems
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| Compute rows in Pascal’s Triangle | | |
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Strings
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Interconvert strings and integers | | |
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| Base conversion | | |
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| Compute the spreadsheet column encoding | | |
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| Replace and remove | | |
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| Solved palindromicity | | |
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| Reverse all the words in a sentence | | |
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| Compute all mnemonics for a phone number | | |
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| The look-and-say problem | | |
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| Convert from Roman to decimal | | |
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| Compute all valid IP addresses | | |
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| Write a string sinusoidally | | |
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| Implement run-length encoding | | |
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| Implement the UNIX `tail` command | | |
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| Find the first occurrence of a substring | | |
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Linked List
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-----------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Merge two sorted lists | Solved | 1hr | iteratively, recursively | Apr 28 | deep dive on recursive solution
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| Reverse a singly linked list | Solved | 30m | Iteratively | May1 | solve with recursion
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| Reverse a single sublist | Attempted | n/a | n/a | May 2 | don't quite get the connection and tail variable
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| Solved for cyclicity | | |
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| Solved for overlapping lists—lists are cycle-free | | | | |
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| Solved for overlapping lists—lists may have cycles | | | | |
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| Delete a node from a singly linked list | | |
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| Remove the *k*th last element from a list | | |
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| Remove duplicates from a sorted list | | | | |
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| Implement cyclic right shift for singly linked lists | | | | |
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| Implement even-odd merge | | | | |
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| Solved whether a singly linked list is palindromic | | | | |
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| Implement list pivoting | | | | |
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| Add list-based integers | | | | |
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Stacks and Queues
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-----------------
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### Stacks
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Implement a stack with max API | | | | |
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| Evaluate RPN expressions | | | | |
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| Solved a string over “{,},(,),[,]†for well-formedness | | | | |
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| Normalize pathnames | | | | |
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| BST keys in sort order | | | | |
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| Search a postings list | | | | |
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| Compute buildings with a sunset view | | | | |
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| Sort a stack | | | | |
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### Queues
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Compute binary tree nodes in order of increasing depth | | | | |
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| Implement a circular queue | | | | |
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| Implement a queue using stacks | | | | |
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| Implement a queue with max API | | | | |
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Binary Trees
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------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Solved if a binary tree is balanced | Solved | 20min | Recursion | Apr30
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| Solved if a binary tree is symmetric | Solved | 1hr | Recursion | May1 | If you need to compare 2 subtrees, use helper(left, right)
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| Compute the lowest common ancestor in a binary tree | Solved | 45min | Recursion | Mar27, May1 |
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| Compute the LCA when nodes have parent pointers | | | | |
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| Sum the root-to-leaf paths in a binary tree | | | | |
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| Find a root to leaf path with specified sum | | | | |
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| Compute the *k*th node in an inorder traversal | | | | |
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| Compute the successor | | | | |
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| Implement an inorder traversal with *O(1)* space | | | | |
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| Reconstruct a binary tree from traversal data | | | | |
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| Reconstruct a binary tree from a preorder traversal with markers | | | | |
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| Form a linked list from the leaves of a binary tree | | | | |
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| Compute the exterior of a binary tree | | | | |
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| Compute the right sibling tree | | | | |
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| Implement locking in a binary tree | | | | |
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Heaps
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-----
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Merge sorted files | | | | |
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| Sort an increasing-decreasing array | | | | |
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| Sort an almost-sorted array | | | | |
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| Compute the *k* closest stars | | | | |
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| Compute the median of online data | | | | |
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| Compute the *k* largest elements in a max-heap | | | | |
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| Implement a stack API using a heap | | | | |
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Searching
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---------
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### Binary Search
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Search a sorted array for first occurrence of *k* | | | | |
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| Search a sorted array for the first element greater than *k* | | | | |
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| Search a sorted array for entry equal to its index | | | | |
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| Search a cyclically sorted array | | | | |
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| Compute the integer square root | | | | |
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| Compute the real square root | | | | |
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### Generalized Search
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Search in a 2D sorted array | Solved | 1hr | Binary Search | Apr 30 |
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| Find the min and max simultaneously | | | | |
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| Find the *k*th largest element | | | | |
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| Compute the optimum mailbox placement | | | | |
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| Find the missing IP address | | | | |
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| Find the duplicate and missing elements | | | | |
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Hash Tables
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-----------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Partition into anagrams | | | | |
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| Solved for palindromic permutations | | | | |
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| Is an anonymous letter constructible? | | | | |
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| Implement an ISBN cache | | | | |
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| Compute the LCA, optimizing for close ancestors | | | | |
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| Compute the *k* most frequent queries | | | | |
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| Find the nearest repeated entries in an array | | | | |
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| Find the smallest subarray covering all values | | | | |
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| Find smallest subarray sequentially covering all values | | | | |
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| Find the longest subarray with distinct entries | | | | |
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| Find the length of a longest contained range | | | | |
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| Compute the average of the top three scores | | | | |
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| Compute all string decompositions | | | | |
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| Find a highest affinity pair | | | | |
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| Solved the Collatz conjecture | | | | |
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| Implement a hash function for chess | | | | |
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Sorting
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-------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Compute the intersection of two sorted arrays | | | | |
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| Implement mergesort in-place | | | | |
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| Count the frequencies of characters in a sentence | | | | |
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| Find unique elements | | | | |
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| Render a calendar | | | | |
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| Sets of disjoint intervals | | | | |
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| Compute the union of intervals | | | | |
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| Partitioning and sorting an array with many repeated entries | | | | |
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| Team photo day—1 | | | | |
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| Implement a fast sorting algorithm for lists | | | | |
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| Compute a salary threshold | | | | |
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Binary Search Trees
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-------------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Solved if a binary tree satisfies the BST property | | | | |
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| Find the first occurrence of a key in a BST | | | | |
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| Find the first key larger than a given value in a BST | | | | |
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| Find the *k* largest elements in a BST | | | | |
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| Compute the LCA in a BST | | | | |
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| Reconstruct a BST from traversal data | | | | |
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| Find the closest entries in three sorted arrays | | | | |
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| Enumerate numbers of the form *a + b√2* | | | | |
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| The most visited pages problem | | | | |
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| Build a minimum height BST from a sorted array | | | | |
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| Insertion and deletion in a BST | | | | |
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| Solved if three BST nodes are totally ordered | | | | |
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| The range lookup problem | | | | |
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| Add credits | | | | |
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| Count the number of entries in an interval | | | | |
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Recursion
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---------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| The Tower of Hanoi problem | | | | |
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| Generate all nonattacking placements of *n*-Queens | | | | |
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| Generate permutations | | | | |
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| Generate the power set | | | | |
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| Generate all subsets of size *k* | | | | |
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| Generate strings of matched parens | | | | |
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| Generate palindromic decompositions | | | | |
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| Generate binary trees | | | | |
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| Implement a Sudoku solver | | | | |
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| Compute a Gray code | | | | |
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| Compute the diameter of a tree | | | | |
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Dynamic Programming
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-------------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Count the number of score combinations | | | | |
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| Compute the Levenshtein distance | | | | |
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| Count the number of ways to traverse a 2D array | | | | |
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| Plan a fishing trip | | | | |
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| Search for a sequence in a 2D array | | | | |
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| The knapsack problem | | | | |
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| Divide the spoils fairly | | | | |
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| The **bedbathandbeyond.com** problem | | | | |
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| Find the minimum weight path in a triangle | | | | |
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| Pick up coins for maximum gain | | | | |
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| Count the number of moves to climb stairs | | | | |
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| Compute the probability of a Republican majority | | | | |
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| The pretty printing problem | | | | |
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| Find the longest nondecreasing subsequence | | | | |
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Greedy Algorithms and Invariants
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--------------------------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Implement Huffman coding | | | | |
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| Compute an optimum assignment of tasks | | | | |
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| Implement a schedule which minimizes waiting time | | | | |
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| The interval covering problem | | | | |
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| The 3-sum problem | | | | |
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| Find the majority element | | | | |
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| The gasup problem | | | | |
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| Compute the maximum water trapped by a pair of vertical lines | | | | |
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| Compute the largest rectangle under the skyline | | | | |
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Graphs
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------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Identify the celebrity | | | | |
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| Search a maze | | |
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| Paint a Boolean matrix | | | | |
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| Compute enclosed regions | | | | |
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| Degrees of connectedness—1 | | | | |
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| Clone a graph | | | | |
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| Making wired connections | | | | |
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| Transform one string to another | | | | |
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| The shorSolved straight-line program for *x^n* | | | | |
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| Team photo day—2 | | | | |
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| Compute a shorSolved path with fewest edges | | | | |
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Parallel Computing
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------------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Implement caching for a multithreaded dictionary | | | | |
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| Analyze two unsynchronized interleaved threads | | | | |
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| Implement synchronization for two interleaving threads | | | | |
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| Implement a thread pool | | | | |
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| Implement asynchronous callbacks | | | | |
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| Implement a Timer class | | | | |
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| The readers-writers problem | | | | |
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| The readers-writers problem with write preference | | | | |
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| Solved the Collatz conjecture in parallel | | | | |
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| Design TeraSort and PetaSort | | | | |
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| Implement distributed throttling | | | | |
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Design Problems
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---------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Design a spell checker | | | | |
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| Design a solution to the stemming problem | | | | |
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| Plagiarism detector | | | | |
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| Pair users by attributes | | | | |
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| Design a system for detecting copyright infringement | | | | |
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| Design *TEX* | | | | |
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| Design a search engine | | | | |
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| Implement PageRank | | | | |
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| Design a scalable priority system | | | | |
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| Create photomosaics | | | | |
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| Implement Mileage Run | | | | |
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| Implement Connexus | | | | |
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| Design an online advertising system | | | | |
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| Design a recommendation system | | | | |
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| Design an optimized way of distributing large files | | | | |
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| Design the World Wide Web | | | | |
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| Estimate the hardware cost of a photo sharing app | | | | |
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Honors Class
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------------
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| Problem | Solved | Time To Solve | Solved Multiple Ways | Last Attempted | Comments
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|--------------------------------------------------------------------------|:------------:|:-------:|
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| Compute the greaSolved common divisor | | | | |
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| Find the first missing positive entry | | | | |
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| Buy and sell a stock *k* times | | | | |
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| Compute the maximum product of all entries but one | | | | |
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| Compute the longest contiguous increasing subarray | | | | |
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| Rotate an array | | | | |
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| Identify positions attacked by rooks | | | | |
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| Justify text | | | | |
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| Reverse sublists *k* at a time | | | | |
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| Implement list zipping | | | | |
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| Copy a postings list | | | | |
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| Compute the median of a sorted circular linked list | | | | |
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| Compute the longest substring with matching parens | | | | |
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| Compute the maximum of a sliding window | | | | |
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| Implement preorder and postorder traversals without recursion | | | | |
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| Compute fair bonuses | | | | |
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| Find *k* elements closest to the median | | | | |
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| Search a sorted array of unknown length | | | | |
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| Search in two sorted arrays | | | | |
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| Find the *k*th largest element—large *n*, small *k* | | | | |
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| Find an element that appears only once | | | | |
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| Find the line through the most points | | | | |
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| Find the shorSolved unique prefix | | | | |
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| Compute the smallest nonconstructible change | | | | |
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| Find the most visited pages in a window | | | | |
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| Convert a sorted doubly linked list into a BST | | | | |
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| Convert a BST to a sorted doubly linked list | | | | |
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| Merge two BSTs | | | | |
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| Solved if a binary tree is an almost BST | | | | |
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| The view from above | | | | |
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| Searching a min-first BST | | | | |
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| Implement regular expression matching | | | | |
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| Synthesize an expression | | | | |
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| Count inversions | | | | |
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| Draw the skyline | | | | |
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| Find the two closest points | | | | |
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| Measure with defective jugs | | | | |
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| Compute the maximum subarray sum in a circular array | | | | |
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| Determine the critical height | | | | |
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| Voltage selection in a logic circuit | | | | |
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| Find the maximum 2D subarray | | | | |
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| Trapping water | | | | |
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| Load balancing | | | | |
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| Search for a pair-sum in an abs-sorted array | | | | |
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| The heavy hitter problem | | | | |
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| Find the longest subarray whose sum ≤ *k* | | | | |
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| Degrees of connectedness—2 | | | | |
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| Compute a minimum delay schedule, unlimited resources | | | | |
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| Road network | | | | |
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| Solved if arbitrage is possible | | | | |
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| The readers-writers problem with fairness | | | | |
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| Implement a producer-consumer queue | | | | |
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------------------------
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**Want to Revisit**
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- binary search
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- longest common subsequence
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------------------------
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**Classic Problems**
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- lowest common ancestor
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- is same tree
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- is subtree
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- invert binary tree
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