Merge pull request #573 from GuoDuanLZ/master

添加 24两两交换链表中的节点，707设计链表 ，206反转链表，19删除链表的倒数第N个节点 Kotlin实现

problems/0019.删除链表的倒数第N个节点.md

@@ -184,6 +184,25 @@ var removeNthFromEnd = function(head, n) {
     return ret.next;
 };
 ```
+Kotlin:
+```Kotlin
+fun removeNthFromEnd(head: ListNode?, n: Int): ListNode? {
+    val pre = ListNode(0).apply {
+        this.next = head
+    }
+    var fastNode: ListNode? = pre
+    var slowNode: ListNode? = pre
+    for (i in 0..n) {
+        fastNode = fastNode?.next
+    }
+    while (fastNode != null) {
+        slowNode = slowNode?.next
+        fastNode = fastNode.next
+    }
+    slowNode?.next = slowNode?.next?.next
+    return pre.next
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

problems/0024.两两交换链表中的节点.md

@@ -228,6 +228,27 @@ var swapPairs = function (head) {
 };
 ```
 
+Kotlin:
+
+```kotlin
+fun swapPairs(head: ListNode?): ListNode? {
+    val dummyNode = ListNode(0).apply { 
+        this.next = head
+    }
+    var cur: ListNode? = dummyNode
+    while (cur?.next != null && cur.next?.next != null) {
+        val temp = cur.next
+        val temp2 = cur.next?.next?.next
+        cur.next = cur.next?.next
+        cur.next?.next = temp
+        cur.next?.next?.next = temp2
+        cur = cur.next?.next
+    }
+    return dummyNode.next
+}
+```
+
+
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

problems/0206.翻转链表.md

@@ -319,7 +319,20 @@ def reverse(pre, cur)
   reverse(cur, tem)	# 通过递归实现双指针法中的更新操作
 end
 ```
-
+Kotlin:
+```Kotlin
+fun reverseList(head: ListNode?): ListNode? {
+    var pre: ListNode? = null
+    var cur = head
+    while (cur != null) {
+        val temp = cur.next
+        cur.next = pre
+        pre = cur
+        cur = temp
+    }
+    return pre
+}
+```
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

problems/0707.设计链表.md

@@ -880,7 +880,73 @@ MyLinkedList.prototype.deleteAtIndex = function(index) {
  * obj.deleteAtIndex(index)
  */
 ```
+Kotlin:
+```kotlin
+class MyLinkedList {
 
+    var next: ListNode? = null
+
+    var size: Int = 0
+
+    fun get(index: Int): Int {
+        if (index + 1 > size) return -1
+        var cur = this.next
+        for (i in 0 until index) {
+            cur = cur?.next
+        }
+        return cur?.`val` ?: -1
+    }
+
+    fun addAtHead(`val`: Int) {
+        val head = ListNode(`val`)
+        head.next = this.next
+        this.next = head
+        size++
+    }
+
+    fun addAtTail(`val`: Int) {
+        val pre = ListNode(0)
+        pre.next = this.next
+        var cur: ListNode? = pre
+        while (cur?.next != null) {
+            cur = cur.next
+        }
+        cur?.next = ListNode(`val`)
+        this.next = pre.next
+        size++
+    }
+
+    fun addAtIndex(index: Int, `val`: Int) {
+        if (index > size) return
+        val pre = ListNode(0)
+        pre.next = this.next
+        var cur:ListNode? = pre
+        for (i in 0 until index) {
+            cur = cur?.next
+        }
+        val temp = cur?.next
+        cur?.next = ListNode(`val`)
+        cur?.next?.next = temp
+        this.next = pre.next
+        size++
+    }
+
+    fun deleteAtIndex(index: Int) {
+        if (index + 1 > size) return
+        val pre = ListNode(0)
+        pre.next = this.next
+        var cur: ListNode? = pre
+        for (i in 0 until index) {
+            cur = cur?.next
+        }
+        val temp = cur?.next?.next
+        cur?.next?.next = null
+        cur?.next = temp
+        this.next = pre.next
+        size--
+    }
+}
+```