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

Example:

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, her h-index is 3.

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

給定一位研究者論文被引用次數的陣列（被引用次數是非負整數）。編寫一個方法，計算出研究者的 h 指數。

h 指數的定義: “h 代表“高引用次數”（high citations），一名科研人員的 h 指數是指他（她）的 （N 篇論文中）至多有 h 篇論文分別被引用了至少 h 次。（其餘的 N - h 篇論文每篇被引用次數不多於 h 次。）”

示例:

輸入: citations = [3,0,6,1,5]
輸出: 3 
解釋: 給定陣列表示研究者總共有 5 篇論文，每篇論文相應的被引用了 3, 0, 6, 1, 5 次。
     由於研究者有 3 篇論文每篇至少被引用了 3 次，其餘兩篇論文每篇被引用不多於 3 次，所以她的 h 指數是 3。

24ms

 1 class Solution {
 2     func hIndex(_ citations: [Int]) -> Int {
 3         let arr = citations.sorted { (num1, num2) -> Bool in
 4             return num1 < num2
 5         }
 6         for i in 0 ..< arr.count {
 7             if arr[i] >= arr.count - i {
 8                 return arr.count - i
 9             }
10         }
11         
12         return 0
13     }
14 }

28ms

 1 class Solution {
 2     func hIndex(_ citations: [Int]) -> Int {
 3         if citations.isEmpty {
 4             return 0
 5         }
 6         let n = citations.count
 7         var res = Array(repeating: 0, count: n + 1)
 8         
 9         for i in citations {
10             if i > n{
11                 res[n] += 1
12             }else {
13                 res[i] += 1
14             }
15         }
16         
17         for i in stride(from: n, to: 0, by: -1) {
18             if res[i] >= i {
19                 return i
20             }
21             res[i-1] += res[i]
22         }
23         
24         
25         return 0
26     }
27 }

28ms

 1 class Solution {
 2     func hIndex(_ citations: [Int]) -> Int {
 3         if citations.isEmpty {
 4             return 0
 5         }
 6         let n = citations.count
 7         var res = Array(repeating: 0, count: n + 1)
 8         
 9         for i in citations {
10             if i > n{
11                 res[n] += 1
12             }else {
13                 res[i] += 1
14             }
15         }
16         
17         for i in stride(from: n, to: 0, by: -1) {
18             if res[i] >= i {
19                 return i
20             }
21             res[i-1] += res[i]
22         }
23         
24         
25         return 0
26     }
27 }

36ms

 1 class Solution {
 2     func hIndex(_ citations: [Int]) -> Int {
 3         let n = citations.count
 4         if (n == 0) {return 0}
 5         var array = Array(repeating:0,count:n + 1)
 6         for i in 0..<n {
 7             if(citations[i] > n) { //所有比n大的都算一起，因為已經不可能是這個了，只計算有幾篇
 8                 array[n] += 1
 9             }
10             else 
11             {
12                 array[citations[i]] += 1             //對應的次數+1
13             }
14         }
15         var t = 0
16         for i in (0...n).reversed() {
17             t = t + array[i] //累加次數
18             if(t >= i) {
19                 return i
20             }
21         }
22         return 0
23     }
24 }

40ms

 1 class Solution {
 2    func hIndex(_ citations: [Int]) -> Int {
 3         guard citations.count > 0 else {
 4             return 0
 5         }
 6         let res = citations.sorted()
 7         for (index,value) in res.enumerated() {
 8             if value >= (res.count - index){
 9                 return res.count - index
10             }
11         }
12     return 0
13     }
14 }