[Swift]LeetCode274.H指数 | H-Index

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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 citations each, and the other N − h papers have no more than h citations each."

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.

---

给定一位研究者论文被引用次数的数组（被引用次数是非负整数）。编写一个方法，计算出研究者的 h 指数。

h 指数的定义: “h 代表“高引用次数”（high citations），一名科研人员的 h 指数是指他（她）的 （N 篇论文中）至多有 h 篇论文分别被引用了至少 h 次。（其余的 N - h 篇论文每篇被引用次数不多于 h 次。）”

示例:

输入: citations = [3,0,6,1,5]
输出: 3 
解释: 给定数组表示研究者总共有 5 篇论文，每篇论文相应的被引用了 3, 0, 6, 1, 5 次。
     由于研究者有 3 篇论文每篇至少被引用了 3 次，其余两篇论文每篇被引用不多于 3 次，所以她的 h 指数是 3。

---

24ms

class Solution {
    func hIndex(_ citations: [Int]) -> Int {
        let arr = citations.sorted { (num1, num2) -> Bool in
            return num1 < num2
        }
        for i in 0 ..< arr.count {
            if arr[i] >= arr.count - i {
                return arr.count - i
            }
        }
        
        return 0
    }
}

---

28ms

class Solution {
    func hIndex(_ citations: [Int]) -> Int {
        if citations.isEmpty {
            return 0
        }
        let n = citations.count
        var res = Array(repeating: 0, count: n + 1)
        
        for i in citations {
            if i > n{
                res[n] += 1
            }else {
                res[i] += 1
            }
        }
        
        for i in stride(from: n, to: 0, by: -1) {
            if res[i] >= i {
                return i
            }
            res[i-1] += res[i]
        }
        
        
        return 0
    }
}

---

28ms

class Solution {
    func hIndex(_ citations: [Int]) -> Int {
        if citations.isEmpty {
            return 0
        }
        let n = citations.count
        var res = Array(repeating: 0, count: n + 1)
        
        for i in citations {
            if i > n{
                res[n] += 1
            }else {
                res[i] += 1
            }
        }
        
        for i in stride(from: n, to: 0, by: -1) {
            if res[i] >= i {
                return i
            }
            res[i-1] += res[i]
        }
        
        
        return 0
    }
}

---

36ms

class Solution {
    func hIndex(_ citations: [Int]) -> Int {
        let n = citations.count
        if (n == 0) {return 0}
        var array = Array(repeating:0,count:n + 1)
        for i in 0..<n {
            if(citations[i] > n) { //所有比n大的都算一起，因为已经不可能是这个了，只计算有几篇
                array[n] += 1
            }
            else 
            {
                array[citations[i]] += 1             //对应的次数+1
            }
        }
        var t = 0
        for i in (0...n).reversed() {
            t = t + array[i] //累加次数
            if(t >= i) {
                return i
            }
        }
        return 0
    }
}

---

40ms

class Solution {
   func hIndex(_ citations: [Int]) -> Int {
        guard citations.count > 0 else {
            return 0
        }
        let res = citations.sorted()
        for (index,value) in res.enumerated() {
            if value >= (res.count - index){
                return res.count - index
            }
        }
    return 0
    }
}