添加（637.二叉树的层平均值）：增加typescript版本

problems/0102.二叉树的层序遍历.md

@@ -941,7 +941,32 @@ var averageOfLevels = function(root) {
 };
 ```
 
+TypeScript：
+
+```typescript
+function averageOfLevels(root: TreeNode | null): number[] {
+    let helperQueue: TreeNode[] = [];
+    let resArr: number[] = [];
+    let total: number = 0;
+    let tempNode: TreeNode;
+    if (root !== null) helperQueue.push(root);
+    while (helperQueue.length > 0) {
+        let length = helperQueue.length;
+        for (let i = 0; i < length; i++) {
+            tempNode = helperQueue.shift()!;
+            total += tempNode.val;
+            if (tempNode.left) helperQueue.push(tempNode.left);
+            if (tempNode.right) helperQueue.push(tempNode.right);
+        }
+        resArr.push(total / length);
+        total = 0;
+    }
+    return resArr;
+};
+```
+
 Swift:
+
 ```swift
 func averageOfLevels(_ root: TreeNode?) -> [Double] {
     var res = [Double]()