275. H-Index II

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Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm?

解法1：

C++

1

Java

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public class Solution {
    public int hIndex(int[] citations) {
        if (citations == null || citations.length == 0) {
            return 0;
        }
        int start = 0;
        int end = citations.length - 1;
        int n = citations.length;
        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (citations[mid] >= n - mid) {
                end = mid;
            }
            else {
                start = mid;
            }
        }
        if (citations[start] >= n - start) {
            return n - start;
        }
        if (citations[end] >= n - end) {
            return n - end;
        }
        return n - end - 1;
    }
}