Merge pull request youngyangyang04#1008 from xiaofei-2020/ts5

添加（0019.删除链表的倒数第N个节点.md）：增加typescript版本

Author: youngyangyang04

problems/0019.删除链表的倒数第N个节点.md

@@ -181,7 +181,71 @@ var removeNthFromEnd = function(head, n) {
     return ret.next;
 };
 ```
+TypeScript:
+
+版本一（快慢指针法）：
+
+```typescript
+function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
+    let newHead: ListNode | null = new ListNode(0, head);
+    let slowNode: ListNode | null = newHead,
+        fastNode: ListNode | null = newHead;
+    for (let i = 0; i < n; i++) {
+        fastNode = fastNode.next;
+    }
+    while (fastNode.next) {
+        fastNode = fastNode.next;
+        slowNode = slowNode.next;
+    }
+    slowNode.next = slowNode.next.next;
+    return newHead.next;
+};
+```
+
+版本二（计算节点总数法）：
+
+```typescript
+function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
+    let curNode: ListNode | null = head;
+    let listSize: number = 0;
+    while (curNode) {
+        curNode = curNode.next;
+        listSize++;
+    }
+    if (listSize === n) {
+        head = head.next;
+    } else {
+        curNode = head;
+        for (let i = 0; i < listSize - n - 1; i++) {
+            curNode = curNode.next;
+        }
+        curNode.next = curNode.next.next;
+    }
+    return head;
+};
+```
+
+版本三（递归倒退n法）：
+
+```typescript
+function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
+    let newHead: ListNode | null = new ListNode(0, head);
+    let cnt = 0;
+    function recur(node) {
+        if (node === null) return;
+        recur(node.next);
+        cnt++;
+        if (cnt === n + 1) {
+            node.next = node.next.next;
+        }
+    }
+    recur(newHead);
+    return newHead.next;
+};
+```
+
 Kotlin:
+
 ```Kotlin
 fun removeNthFromEnd(head: ListNode?, n: Int): ListNode? {
     val pre = ListNode(0).apply {