Merge pull request youngyangyang04#1012 from xiaofei-2020/ts7

添加（0142.环形链表II.md）：增加typescript版本

Author: youngyangyang04

problems/0142.环形链表II.md

@@ -294,7 +294,30 @@ var detectCycle = function(head) {
 };
 ```
 
+TypeScript：
+
+```typescript
+function detectCycle(head: ListNode | null): ListNode | null {
+    let slowNode: ListNode | null = head,
+        fastNode: ListNode | null = head;
+    while (fastNode !== null && fastNode.next !== null) {
+        slowNode = (slowNode as ListNode).next;
+        fastNode = fastNode.next.next;
+        if (slowNode === fastNode) {
+            slowNode = head;
+            while (slowNode !== fastNode) {
+                slowNode = (slowNode as ListNode).next;
+                fastNode = (fastNode as ListNode).next;
+            }
+            return slowNode;
+        }
+    }
+    return null;
+};
+```
+
 Swift:
+
 ```swift
 class Solution {
     func detectCycle(_ head: ListNode?) -> ListNode? {