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