右旋字符串 swift版本

problems/kamacoder/0055.右旋字符串.md

@@ -350,7 +350,29 @@ function reverseStr(s, start, end) {
 
 
 ### Swift:
+```swift
+func rotateWords(_ s: String, _ k: Int) -> String {
+    var chars = Array(s)
+    // 先反转整体
+    reverseWords(&chars, start: 0, end: s.count - 1)
+    // 反转前半段
+    reverseWords(&chars, start: 0, end: k - 1)
+    // 反转后半段
+    reverseWords(&chars, start: k, end: s.count - 1)
+    return String(chars)
+}
 
+// 反转start...end 的字符数组
+func reverseWords(_ chars: inout [Character], start: Int, end: Int) {
+    var left = start
+    var right = end
+    while left < right, right < chars.count {
+        (chars[left], chars[right]) = (chars[right], chars[left])
+        left += 1
+        right -= 1
+    }
+}
+```
 
 
 ### PHP：