129. 求根节点到叶节点数字之和

Author: w2xi

README.md

@@ -68,6 +68,7 @@
 |119|[杨辉三角 II](https://leetcode.cn/problems/pascals-triangle-ii/)|[JavaScript](./algorithms/pascals-triangle-ii.js)|Easy|
 |124|[二叉树中的最大路径和](https://leetcode.cn/problems/binary-tree-maximum-path-sum/)|[JavaScript](./algorithms/binary-tree-maximum-path-sum.js)|Hard|
 |125|[验证回文串](https://leetcode.cn/problems/valid-palindrome/)|[JavaScript](./algorithms/valid-palindrome.js)|Easy|
+|129|[求根节点到叶节点数字之和](https://leetcode.cn/problems/sum-root-to-leaf-numbers/)|[JavaScript](./algorithms/sum-root-to-leaf-numbers.js)|Medium|
 |136|[只出现一次的数字](https://leetcode-cn.com/problems/single-number/)|[JavaScript](./algorithms/single-number.js)|Easy|
 |141|[环形链表](https://leetcode-cn.com/problems/linked-list-cycle/)|[JavaScript](./algorithms/linked-list-cycle.js)|Easy|
 |142|[环形链表 II](https://leetcode.cn/problems/linked-list-cycle-ii/)|[JavaScript](./algorithms/linked-list-cycle-ii.js)|Medium|

algorithms/sum-root-to-leaf-numbers.js

@@ -0,0 +1,29 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * 129. 求根节点到叶节点数字之和
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var sumNumbers = function (root) {
+  let sum = 0;
+  const dfs = (root, val = 0) => {
+    if (root) {
+      val = val * 10 + root.val;
+      if (!root.left && !root.right) {
+        sum += val;
+      }
+      dfs(root.left, val);
+      dfs(root.right, val);
+    }
+  };
+  dfs(root);
+
+  return sum;
+};