题目描述

寻找 0 ~ n-1 中缺失的数字

思路：左边 $q[i] == i$ ，右边 $q[i] != i$ 。这就是二分性质的分界点

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