剑指OFFER----面试题53

链接：https://leetcode-cn.com/problems/que-shi-de-shu-zi-lcof/

代码

class Solution {
public:
    int missingNumber(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) r = mid;
            else l = mid + 1;
        }

        if (nums[r] == r) r++;
        return r;
    }
};