feat: binary-tree-level-order-traversal

Author: junbinding

bfs.binary-tree-level-order-traversal.py

@@ -0,0 +1,59 @@
+from typing import List
+from collections import deque
+
+
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+class Solution:
+    """
+    102. 二叉树的层序遍历
+    https://leetcode-cn.com/problems/binary-tree-level-order-traversal/
+    给你一个二叉树，请你返回其按 层序遍历 得到的节点值。 （即逐层地，从左到右访问所有节点）。
+    """
+    # dfs
+    def levelOrder(self, root: TreeNode) -> List[List[int]]:
+        res = []
+        def dfs(level, node):
+            if not node:
+                return
+
+            if len(res) == level:
+                res.append([])
+
+            res[level].append(node.val)
+            dfs(level + 1, node.left)
+            dfs(level + 1, node.right)
+
+        dfs(0, root)
+        return res
+
+    # bfs
+    def levelOrderByBfs(self, root: TreeNode) -> List[List[int]]:
+        res = []
+        queue = deque()
+        queue.append(root)
+
+        while queue:
+            size = len(queue)
+            level = []
+            for _ in range(size):
+                cur = queue.popleft()
+                if not cur:
+                    continue
+
+                level.append(cur.val)
+                queue.append(cur.left)
+                queue.append(cur.right)
+
+            if level:
+                res.append(level)
+
+        return res
+
+
+