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public int hIndex(int[] citations) {
	int len = citations.length;
	int lo = 0, hi = len - 1;
	while (lo <= hi) {
		int med = (hi + lo) / 2;
		if (citations[med] == len - med) {
			return len - med;
		} else if (citations[med] < len - med) {
			lo = med + 1;
		} else { 
			//(citations[med] > len-med), med qualified as a hIndex,
		    // but we have to continue to search for a higher one.
			hi = med - 1;
		}
	}
	return len - lo;
}

public class Solution {
    public int hIndex(int[] citations) {
        if (citations == null || citations.length < 1) return 0;
        int i = 0;
        int len = citations.length;
        while (i < len && citations[len - 1 - i] > i) {
            i++;
        }
        return i;
    }
}