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0540 - Single Element in a Sorted Array (Medium)

Problem Statement​

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

Return the single element that appears only once.

Your solution must run in O(log n) time and O(1) space.

Example 1:

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

Example 2:

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

Constraints:

  • 1 <= nums.length <= 105
  • 0 <= nums[i] <= 105
Written by @wingkwong
class Solution {
public:
    int singleNonDuplicate(vector<int>& nums) {
        // init possible boundary
        int n = nums.size(), l = 0, r = n - 1;
        while (l < r) {
            // get the middle one
            // for even number of elements, take the lower one
            int m = l + (r - l) / 2;
            // handle case like [3,3,7,7,10,11,11]
             m -= m & 1;
            // exclude m
            if (nums[m] == nums[m + 1]) l = m + 2;
            // include m
            else r = m;
        }
        return nums[l];
    }
};