H-Index Solutions in C++

// Source : https://leetcode.com/problems/h_index/
// Author : Calinescu Valentin, Hao Chen
// Date   : 2015-10-22





/* 
 * Solutions
 * =========
 *
 * A simple solution would be to sort the vector and then run through it starting with
 * the last element. At every step we need to check whether this element is not less than
 * the remaining number of elements bigger than it(including itself) and all the values of
 * the other elements smaller than it are not more than that number. The h_index is this
 * number of elements bigger than it(including itself).
 * 
 * Time Complexity: O(N log N)
 * Space Complexity: O(1)
 * 
 */
#include <algorithm>
class Solution {
public:
    int hIndex(vector<int>& citations) {
        return hIndex02(citations);
        return hIndex01(citations);
    }
    int hIndex01(vector<int>& citations) {
        sort(citations.begin(), citations.end());
        int h_index = 0;
        for(int i = citations.size() - 1; i >= 0; i--)
            if(citations[i] >= citations.size() - i && (i - 1 < 0 || citations[i - 1] <= citations.size() - i))
                h_index = citations.size() - i;
        return h_index;
    }

    // same solution but a bit different implemtation
    int hIndex02(vector<int>& citations) {
        sort(citations.begin(), citations.end());
        int n = citations.size();
        for (int i=0; i<n; i++){
            if (citations[i] >= n-i){
                return n-i;
            }
        }
        return 0;
    }

};