257

Author: tech-cow

README.md

@@ -89,3 +89,4 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |-----|-------| -------- | ---- | ------|------------|---|-----|
 |108|[Convert Sorted Array to Binary Search Tree](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/#/solutions)| [Python [Yu]](./tree/Yu/108.py) | _O(N)_| _O(N)_  | Easy | |[公瑾讲解](https://www.youtube.com/watch?v=lBrb4fXPcMM)|
 |563|[Binary Tree Tilt](https://leetcode.com/problems/binary-tree-tilt/#/description)| [Python [Yu]](./tree/Yu/563.py) | _O(N)_| _O(1)_  | Easy | |[公瑾讲解](https://youtu.be/47FQVP4ynk0)|
+|257|[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/#/description)| [Python [Yu]](./tree/Yu/257.py) | _O(N)_| _O(N)_  | Easy | |[公瑾讲解](https://youtu.be/Zr_7qq2f16k)|

tree/Yu/257.py

@@ -0,0 +1,33 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# Author: Yu Zhou
+
+# 257. Binary Tree Paths
+
+# 思路：
+# DFS + Stack
+
+class Solution(object):
+    def binaryTreePaths(self, root):
+        """
+        :type root: TreeNode
+        :rtype: List[str]
+        """
+        stack = [(root, "")]
+        res = []
+
+        # Edge Case
+        if not root:
+            return []
+
+        # res: ["1->3", "1->2->5"]
+        while stack:
+            node, strr = stack.pop()
+            if not node.left and not node.right:
+                res.append(strr + str(node.val))
+            if node.left:
+                stack.append((node.left, strr + str(node.val) + "->"))
+            if node.right:
+                stack.append((node.right, strr + str(node.val) + "->"))
+        return res