540. Single Element in a Sorted Array

Problem:

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:

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.

思路：

Solution (C++):

int singleNonDuplicate(vector<int>& nums) {
    int n = nums.size();
    int low = 0, high = n - 1;
    
    while (low < high) {
        int mid = low + (high - low) / 2;
        if (mid%2 == 0) {
            if (nums[mid] == nums[mid-1])  high = mid - 2;
            else if (nums[mid] == nums[mid+1])  low = mid + 2;
            else return nums[mid];
        } else {
            if (nums[mid] == nums[mid-1])  low = mid + 1;
            else if (nums[mid] == nums[mid+1])  high = mid - 1;
        }
    }
    return nums[low];
}

性能：

Runtime: 8 ms  Memory Usage: 7.5 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB