[leetcode] 275. H-Index II

原创

是念 2022-08-11 17:19:59 博主文章分类：C++ ©著作权

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Description

Given an array of citations sorted in ascending order (each citation is a non-negative integer) of a researcher, write a function to compute the researcher’s h-index.

According to the definition of h-index on Wikipedia: “A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each.”

Example:

Input: citations = [0,1,3,5,6]
Output: 3 
Explanation: [0,1,3,5,6] means the researcher has 5 papers in total and each of them had 
             received 0, 1, 3, 5, 6 citations respectively. 
             Since the researcher has 3 papers with at least 3 citations each and the remaining 
             two with no more than 3 citations each, her h-index is 3.

Note:

If there are several possible values for h, the maximum one is taken as the h-index.

Follow up:

This is a follow up problem to H-Index, where citations is now guaranteed to be sorted in ascending order.
Could you solve it in logarithmic time complexity?

分析

题目的意思是：给定一个排序的数组，计算其h-index。

我们最先初始化left和right为0和数组长度len-1，然后取中间值mid，比较citations[mid]和len-mid做比较，
如果前者大，则right移到mid之前，反之right移到mid之后，终止条件是left>right，最后返回len-left即可.

代码

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n=citations.size();
        int i=0;
        int j=n-1;
        while(i<=j){
            int mid=(i+j)/2;
            if(citations[mid]==n-mid){
                return n-mid;
            }else if(citations[mid]>n-mid){
                j=mid-1;
            }else{
                i=mid+1;
            }
        }
        return n-i;
    }
};