LeetCode 540. Single Element in a Sorted Array

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题目

You are given a sorted array consisting of only integers where every element appears exactly twice, except for one element which appears exactly once. Find this single element that appears only once.

Example 1:

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Input: [1,1,2,3,3,4,4,8,8]
Output: 2

Example 2:

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Input: [3,3,7,7,10,11,11]
Output: 10

Note: Your solution should run in O(log n) time and O(1) space.

思路

sorted array + O(log n) time == 二分查找…
可以记一些常用的代替算术运算符的操作:

  • (l+r)/2 ==> (l+r)>>1
  • l%2 == 1 ==> l&1 == 1

代码

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class Solution(object):
    def singleNonDuplicate(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        l, r = 0, len(nums)-1
        while l < r:
            mid = (l+r)>>1
            if nums[mid] == nums[mid-1]:
                if (mid-1) & 1:
                    r = mid-2
                else:
                    l = mid+1
            elif nums[mid] == nums[mid+1]:
                if mid & 1:
                    r = mid-1
                else:
                    l = mid+2
            else:
                return nums[mid]
        return nums[l]