127 lines
2.8 KiB
Python
127 lines
2.8 KiB
Python
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class DLLNode:
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def __init__(self, key, val):
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self.key = key
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self.val = val
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self.next = None
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self.prev = None
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class LruCache:
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def __init__(self, capacity):
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# hashtable for fast lookup
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self.hashmap = {}
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self.capacity = capacity
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self.head = None # most recently used item
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self.tail = None # least recently used item
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def get(self, key):
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## TODO
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return hashmap.get(key)
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'''
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put will need to put elements into
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'''
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def put(self, key, val):
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# if capacity is reached, evict last elem
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# if len(self.hashmap)==self.capacity:
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# print "capacity reached"
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# lastNode = self.tail
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# self.tail = lastNode.prev
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# lastNode.prev = None
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# key exists in hash table
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if key in self.hashmap:
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# update node's value
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currentNode = self.hashmap[key]
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currentNode.val = val
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# if current node is not head
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if not currentNode == self.head:
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# remove yourself from list
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if currentNode.prev:
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currentNode.prev.next = currentNode.next
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if currentNode.next:
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currentNode.next.prev = currentNode.prev
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# add to beginning of list
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currentNode.next = self.head
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self.head = currentNode # reassign head node
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# if current node is tail node
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if currentNode == self.tail:
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self.tail = currentNode.prev
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currentNode.prev = None
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# not in hash table
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else:
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# put it at the front of the list
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newNode = DLLNode(key, val)
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if not self.head:
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self.head = newNode
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self.tail = newNode
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else:
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newNode.next = self.head
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self.head.prev = newNode
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self.head = newNode # reassign head node
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# add node to hash table
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self.hashmap[key] = newNode
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def show(self):
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# print hashmap
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print( self.hashmap )
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print ("head: " + str(self.head.val))
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print ("tail: " + str(self.tail.val))
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# iterate doubly linked list
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node = self.head
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while node:
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print( node.val )
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node = node.next
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print("")
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cache = LruCache(3)
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cache.put(1,10)
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cache.put(2,20)
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cache.put(3,30)
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cache.show()
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cache.put(2, 200) # move elem to head
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cache.show()
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cache.put(1, 100) # move end elem to beginning
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cache.show()
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cache.put(1, 1000) # move start elem to beginning (breaks)
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cache.show()
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cache.put(4, 40)
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cache.show() # test new eviction logic
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