LeetCode:H-Index II

Posted 2020-07-19 walker lee

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:

1. Expected runtime complexity is in O(log n) and the input is sorted.

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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;
    }
}