H-Index

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 leasth citations each, and the other N − h papers have no more thanh 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 least3 citations each and the remaining two with no more than3 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.

Bucket sort

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int n = citations.size();
        int dp[n + 1];
        memset(dp, 0, sizeof(dp));
        for(int i = 0; i < n; i++){
            if(citations[i] > n){
                dp[n]++;
            }else{
                dp[citations[i]]++;
            }
        }
        int total = 0;
        for(int i = n; i >= 0; i--){
            total += dp[i];
            if(total >= i){
                return i;
            }
        }
    }
};

o(nlogn) approach

class Solution {
public:
    int hIndex(vector<int>& citations) {
        int ans = 0;
        if(citations.size() == 0) return 0;
        sort(citations.begin(), citations.end());
        for(int i = citations.size() - 1; i >= 0; i--){
            int v = citations[i];
            if(v <= citations.size() - i - 1){
                return citations.size() - i - 1;
            }
        }
        return citations.size();
    }
};