Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm?
如果citations是升序排列，则可以使用二分查找。这道题是让找有几篇论文的引用超过了几次。判断条件为：citations[mid] < (len - mid)，最后的返回值是：len - 1 - left。代码如下：
public class Solution {
public int hIndex(int[] citations) {
int len = citations.length;
int left = -1, right = len;
while (left + 1 < right) {
int mid = left + (right - left) / 2;
if (citations[mid] < (len - mid)) {
left = mid;
} else {
right = mid;
}
}
return len - 1 - left;
}
}
