solve(w14): 102. Binary Tree Level Order Traversal

Author: seungriyou

binary-tree-level-order-traversal/seungriyou.py

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+# https://leetcode.com/problems/binary-tree-level-order-traversal/
+
+from typing import Optional, List
+
+# 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
+
+class Solution:
+    def levelOrder_bfs(self, root: Optional[TreeNode]) -> List[List[int]]:
+        """
+        [Complexity]
+            - TC: O(n)
+            - SC: O(width) (최악의 경우 O(n)) (결과 res 제외)
+
+        [Approach]
+            레벨 별로 BFS로 접근
+        """
+        if not root:
+            return []
+
+        res, level = [], [root]
+
+        while level:
+            # res에 현재 level 내 node value 추가
+            res.append([node.val for node in level])
+
+            # next level의 node로 level 업데이트
+            level = [child for node in level for child in (node.left, node.right) if child]
+            # next_level = []
+            # for node in level:
+            #     if node.left:
+            #         next_level.append(node.left)
+            #     if node.right:
+            #         next_level.append(node.right)
+            # level = next_level
+
+        return res
+
+    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
+        """
+        [Complexity]
+            - TC: O(n)
+            - SC: O(height) (call stack) (결과 res 제외)
+
+        [Approach]
+            레벨 별로 DFS로 접근
+        """
+        if not root:
+            return []
+
+        res = []
+
+        def dfs(node, level):
+            # base condition (각 level의 첫 시작)
+            if len(res) == level:
+                res.append([])
+
+            # 현재 level에 node.val 추가
+            res[level].append(node.val)
+
+            # node의 child에 대해 다음 level로 진행
+            if node.left:
+                dfs(node.left, level + 1)
+            if node.right:
+                dfs(node.right, level + 1)
+
+        dfs(root, 0)
+
+        return res