Merge pull request wangzheng0822#88 from jerryderry/counting-sort-swift

Counting sort in swift

Author: wangzheng0822

swift/14_sorts/CountingSort.swift

@@ -0,0 +1,33 @@
+//
+// CountingSort.swift
+// algo
+//
+// Created by Wenru Dong on 2018/10/18.
+// Copyright © 2018年 Wenru Dong. All rights reserved.
+//
+
+import Foundation
+
+// 假设数组中储存的都是非负整数
+public func countingSort(_ a: inout [Int]) {
+ if a.count <= 1 { return }
+ 
+ var counts = Array(repeating: 0, count: a.max()! + 1)
+ for num in a {
+ counts[num] += 1
+ }
+ for i in 1..<counts.count {
+ counts[i] = counts[i-1] + counts[i]
+ }
+ 
+ var aSorted = Array(repeating: 0, count: a.count)
+ for num in a.reversed() {
+ let index = counts[num] - 1
+ aSorted[index] = num
+ counts[num] -= 1
+ }
+ 
+ for (i, num) in aSorted.enumerated() {
+ a[i] = num
+ }
+}