# 274. H-Index

274. H-Index

[TOC]

## 题目内容

Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper, return compute the researcher’s h-index.

According to the definition of h-index on Wikipedia: A scientist has an index h if h of their n papers have at least h citations each, and the other n − h papers have no more than h citations each.

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

Example 1:

Input: citations = [3,0,6,1,5]
Output: 3
Explanation: [3,0,6,1,5] 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, their h-index is 3.
Example 2:

Input: citations = [1,3,1]
Output: 1

Constraints:

n == citations.length
1 <= n <= 5000
0 <= citations[i] <= 1000

## 方法

### 排序

``````class Solution {
fun hIndex(citations: IntArray): Int {
citations.sort()
var h = 0
var i = citations.size - 1;
while (i >= 0 && citations[i] > h) {
h++;
i--;
}
return h;
}
}
``````

### 计数排序

``````class Solution {
fun hIndex(citations: IntArray): Int {
val n = citations.size
val counter = IntArray(n + 1)

counter.forEachIndexed { index, value ->
if (index >= n) {
return@forEachIndexed
}
if (citations[index] >= n) {
counter[n]++;
} else {
counter[citations[index]]++;
}
}

var tot = 0;

var i = n
while (i >= 0) {
tot += counter[i];
if (tot >= i) {
return i
}
i--
}
return 0
}
}
``````