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.

思想：用的二分法 注意索引的左右判断,二分的奇偶判断

AC代码：时间o(logn) 空间o(1)

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