540. Single Element in a Sorted Array

Given a sorted array consisting of only integers where every element appears twice except for one element which appears once. Find this single element that appears only once.

Example 1:

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

 

Example 2:

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

 

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

 

一个有序数组只有一个数不出现两次，找出这个数。要求以 O(logN) 时间复杂度进行求解。

 

C++:

class Solution {
public:
    int singleNonDuplicate(vector<int>& nums) {
        int left = 0 ;
        int right = nums.size() - 1 ;
        while(left < right){
            int mid = left + (right - left) / 2 ;
            if (mid%2 == 1){
                mid-- ;
            }
            if (nums[mid] == nums[mid+1]){
                left = mid + 2 ;
            }else{
                right = mid ;
            }
        }
        return nums[left] ;
    }
};