feat(leetcode;): 144.二叉树的前序遍历

144.二叉树的前序遍历

Signed-off-by: Ching <loooching@gmail.com>

144.二叉树的前序遍历.py

@@ -0,0 +1,45 @@
+#
+# @lc app=leetcode.cn id=144 lang=python3
+#
+# [144] 二叉树的前序遍历
+#
+
+# @lc code=start
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+from typing import List
+
+from utils import *
+
+
+class Solution:
+    def preorderTraversal(self, root: TreeNode) -> List[int]:
+        res = []
+        stack = []
+        if root:
+            stack.append(root)
+        while stack:
+            node = stack[-1]
+            if node:
+                stack.pop()
+                if node.right:
+                    stack.append(node.right)
+                if node.left:
+                    stack.append(node.left)
+                stack.append(node)
+                stack.append(None)
+            else:
+                stack.pop()
+                node = stack.pop()
+                res.append(node.val)
+        return res
+
+
+s = Solution()
+root = generate_tree([1, None, 2])
+s.preorderTraversal(root)
+# @lc code=end