62 lines
1.1 KiB
Markdown
62 lines
1.1 KiB
Markdown
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---
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layout: page
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title: Single Number II
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last_solved: 2020-06-22
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category: bit manipulation
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leetcode_url: https://leetcode.com/problems/single-number-ii
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status: Attempted
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---
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Problem
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-------
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```
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Given a non-empty array of integers, every element appears three times except for one, which appears exactly once. Find that single one.
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Note:
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Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
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Example 1:
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Input: [2,2,3,2]
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Output: 3
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Example 2:
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Input: [0,1,0,1,0,1,99]
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Output: 99
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```
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Solution
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----------
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If a number appears 3 times, then its sum of bits will be of the form ```3 * n```.
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But if it only appears once, then it's sum of bits will be ```n```.
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So iterate thru all 32 bits of integers, adding their sums, mod it by 3 and the remaining will be the answer.
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Let's take [2,2,3,2] for example.
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```
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0 1 0 | 2
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0 1 0 | 2
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0 1 0 | 2
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1 0 0 | 3
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---------------
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1 3 0 sum of each digit column
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1 % 3 => 1
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3 % 3 => 0
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0 % 0 => 0
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The answer is 3
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```
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{% highlight python %}
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{% endhighlight %}
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![image1]()
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