Merge pull request #629 from qxuewei/master

添加 19.删除链表的倒数第N个节点 Swift版本 & 添加 24. 两两交换链表中的节点 Swift版本

problems/0019.删除链表的倒数第N个节点.md

@@ -204,6 +204,31 @@ fun removeNthFromEnd(head: ListNode?, n: Int): ListNode? {
 }
 ```
 
+Swift：
+```swift
+func removeNthFromEnd(_ head: ListNode?, _ n: Int) -> ListNode? {
+    if head == nil {
+        return nil
+    }
+    if n == 0 {
+        return head
+    }
+    let dummyHead = ListNode(-1, head)
+    var fast: ListNode? = dummyHead
+    var slow: ListNode? = dummyHead
+    // fast 前移 n
+    for _ in 0 ..< n {
+        fast = fast?.next
+    }
+    while fast?.next != nil {
+        fast = fast?.next
+        slow = slow?.next
+    }
+    slow?.next = slow?.next?.next
+    return dummyHead.next
+}
+```
+
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 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

problems/0024.两两交换链表中的节点.md

@@ -256,6 +256,27 @@ fun swapPairs(head: ListNode?): ListNode? {
 }
 ```
 
+Swift:
+```swift
+func swapPairs(_ head: ListNode?) -> ListNode? {
+    if head == nil || head?.next == nil {
+        return head
+    }
+    let dummyHead: ListNode = ListNode(-1, head)
+    var current: ListNode? = dummyHead
+    while current?.next != nil && current?.next?.next != nil {
+        let temp1 = current?.next
+        let temp2 = current?.next?.next?.next
+        
+        current?.next = current?.next?.next
+        current?.next?.next = temp1
+        current?.next?.next?.next = temp2
+        
+        current = current?.next?.next
+    }
+    return dummyHead.next
+}
+```
 
 
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