LeetCode 275. H-Index II

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class Solution {
public:
    int hIndex(vector<int>& citations) {
        int i = citations.size() - 1, h = 0;
        while (i >= 0 && citations[i] > h) ++h, --i;
        return h;
    }
};
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class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n = citations.size(), l = 0, r = n;
        auto check = [&](int h) {
            int idx = lower_bound(citations.begin(), citations.end(), h) - citations.begin();
            return n - idx >= h;
        };
        while (l < r) {
            int mid = l + r + 1 >> 1;
            if (check(mid)) l = mid;
            else r = mid - 1;
        }
        return l;
    }
};