add maximum-depth-of-binary-tree solution

Author: jongwanra

maximum-depth-of-binary-tree/jongwanra.py

@@ -0,0 +1,60 @@
+"""
+[Problem]
+https://leetcode.com/problems/maximum-depth-of-binary-tree/description/
+
+Return maximum depth of binary tree
+0 < the number of nodes < 10,000
+
+[Brainstorming]
+DFS를 이용해서 구해보자.
+이진 트리에서 전체 탐색을 DFS로 진행했을 떄 시간 복잡도는 O(N)으로 판단된다.
+
+[Complexity]
+N is the number of nodes
+Time: O(N)
+Space: O(N)
+  -> node의 개수 만큼 call stack이 쌓임
+"""
+
+from typing import Optional
+# 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 maxDepth(self, root: Optional[TreeNode]) -> int:
+        answer = 0
+
+        def dfs(depth, node:Optional[TreeNode])->None:
+            nonlocal answer
+            if not node.left and not node.right:
+                answer = max(answer, depth)
+                return
+
+            if node.left:
+                dfs(depth + 1, node.left)
+            if node.right:
+                dfs(depth + 1, node.right)
+
+        if not root:
+            return answer
+        dfs(1, root)
+        return answer
+
+
+class AnotherSolution:
+    """
+    ref: leetcode
+
+    [Complexity]
+    Time: O(N)
+    Space: O(N)
+    """
+    def maxDepth(self, root:Optional[TreeNode])-> int:
+        if not root:
+            return 0
+        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))
+
+