Smallest String Starting From Leaf

Author: w2xi

README.md

@@ -56,4 +56,5 @@
 |897|[递增顺序搜索树](https://leetcode.cn/problems/increasing-order-search-tree/)|[JavaScript](./algorithms/increasing-order-search-tree.js)|Easy|
 |912|[排序数组](https://leetcode.cn/problems/sort-an-array/)|[JavaScript](./algorithms/sort-an-array.js)|Medium|
 |965|[单值二叉树](https://leetcode.cn/problems/univalued-binary-tree/)|[JavaScript](./algorithms/univalued-binary-tree.js)|Easy|
+|988|[从叶结点开始的最小字符串](https://leetcode.cn/problems/smallest-string-starting-from-leaf/)|[JavaScript](./algorithms/smallest-string-starting-from-leaf.js)|Medium|
 |面试题 04.12|[面试题 04.12. 求和路径](https://leetcode.cn/problems/paths-with-sum-lcci/)|[JavaScript](./algorithms/paths-with-sum-lcci.js)|Medium|

algorithms/smallest-string-starting-from-leaf.js

@@ -0,0 +1,32 @@
+/**
+ * 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)
+ * }
+ */
+/**
+ * 从叶结点开始的最小字符串
+ * @param {TreeNode} root
+ * @return {string}
+ */
+var smallestFromLeaf = function (root) {
+  const str = "abcdefghijklmnopqrstuvwxyz";
+  let minPath = "";
+  const dfs = (node, path = "") => {
+    if (node) {
+      path = str[node.val] + path;
+      // leaf node
+      if (!node.left && !node.right) {
+        if (!minPath || minPath > path) {
+          minPath = path;
+        }
+      }
+      dfs(node.left, path);
+      dfs(node.right, path);
+    }
+  };
+  dfs(root);
+  return minPath;
+};