104_Maximum Depth of Binary Tree

104. Maximum Depth of Binary Tree

Level: easy

Tag: tree, dfs

Question

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Solution 1: recursive

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root:
            return 0

        l = self.maxDepth(root.left)
        r = self.maxDepth(root.right)
        res = 1 + max(l, r)
        return res

Solution 2: iterative (Depth first search, using stack)

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        res = 0
        stack = [(root, 0)]
        if not root:
            return res

        while stack:
            node, depth = stack.pop()
            if node.right:
                stack.append((node.right, depth + 1))
            if node.left:
                stack.append((node.left, depth + 1))
            res = max(res, depth + 1)
        return res