h-index

https://leetcode.com/problems/h-index/

https://leetcode.com/mockinterview/session/result/xjcpjlh/

看了hint，不然的话，可能用的是排序的方法，O(NlgN)，现在的方法用了extra space，但是时间复杂度是O(N).

package com.company;

import java.util.*;

// https://discuss.leetcode.com/topic/32272/share-my-greedy-solution/2

class Solution {
    public int hIndex(int[] citations) {
        int[] rec = new int[citations.length];

        for (int i=0; i<citations.length; i++) {
            if (citations[i] >= 1 &&  citations[i] <= citations.length) {
                rec[citations[i]-1]++;
            }
            else if (citations[i] > citations.length) {
                rec[citations.length-1]++;
            }
        }

        int count = 0;
        for (int i=citations.length; i>0; i--) {
            count += rec[i-1];
            if (count >= i) {
                return i;
            }
        }
        return 0;
    }
}

public class Main {

    public static void main(String[] args) throws InterruptedException {

        System.out.println("Hello!");
        Solution solution = new Solution();

        // Your Codec object will be instantiated and called as such:
        int[] citations = {3, 0, 6, 1, 5};

        int ret = solution.hIndex(citations);
        System.out.printf("ret:%d\n", ret);

        System.out.println();

    }

}