H-Index和H-Index II

H-Index

原题

Given an array of citations (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."For example, given citations = [3, 0, 6, 1, 5], which means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 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, his h-index is 3.Note: If there are several possible values for h, the maximum one is taken as the h-index.

思路

直接按wiki上的说来弄.

code

class Solution {public:    int hIndex(vector<int>& citations) {        sort(citations.begin(), citations.end(), greater<int>());        int i;        for(i = 0; i < citations.size(); i++) {            if(citations[i] <= i) return i;        }        return i;    }};

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H-Index II

原题

Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm?

思路

类似二分查找.

code

class Solution {public:    int hIndex(vector<int>& citations) {        int len = citations.size();        int l = 0, r = len - 1;        while(l <= r) {            int m = l + ((r - l) >> 1);            int m2 = len - m;            if(m2 <= citations[m]) {                r = m - 1;            } else {                l = m + 1;            }        }        return len - l;    }};