class Solution {
public:
    int hIndex(vector<int>& citations) {
        int h = 0, n = citations.size();
        int left = 0, right = n - 1;
        int ans = 0;    //初值为0可以处理一些特殊情况
        while(left <= right){
            int mid = (left  + right) / 2;
            //按提议要求，h篇至少引用了h次
            //因为原数组是升序，越往后越大，那么第i个元素 = num[i]代表n - i个元素大于等于 num[i]
            //所以citations[mid] >= n - mid
            if(citations[mid] >= n - mid){
                right = mid - 1;
                ans = n - mid;
            }
            else
                left = mid + 1;
        }
        return ans;
    }
};

Accepted
83/83 cases passed (12 ms)
Your runtime beats 90.17 % of cpp submissions
Your memory usage beats 46.97 % of cpp submissions (18.2 MB)