LeetCode:H-Index II

H-Index II

Total Accepted: 24331 Total
Submissions: 74459 Difficulty: Medium

Follow up for H-Index:
What if the 

citations

 array is sorted in ascending order? Could you optimize your algorithm?
Hint:
Expected runtime complexity is in O(log n) and the input is sorted.

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 (M) H-Index

思路：

承接上题【】，与上题不同之处在于已经是排序的，因此通过二分找到临界点即可。

java code:

public class Solution {
public int hIndex(int[] citations) {

if(citations == null || citations.length == 0) return 0;

int len = citations.length;
int lo = 0, hi = len-1;

while(lo <= hi) {
int mid = lo + (hi-lo)/2;

if(citations[mid] == len - mid)
return len-mid;
else if(citations[mid] >= len - mid)
hi = mid - 1;
else
lo = mid + 1;
}

return len-lo;
}
}