104. Maximum Depth of Binary Tree

February 14, 2022

Given the root of a binary tree, return its maximum depth. A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1: Input: root = [3,9,20,null,null,15,7] Output: 3 Example 2: Input: root = [1,null,2] Output: 2

Constraints:

The number of nodes in the tree is in the range [0, 104].
-100 <= Node.val <= 100

code

class Solution:
    def maxDepth(self, root: TreeNode) -> int:
        if not root:
            return 0
        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))

c iteration

class Solution:
    def maxDepth(self, root):
        if not root: return 0 
        level = [root]; depth = 0
        while level:
            depth += 1
            level = [i for n in level for i in (n.left, n.right) if i]
        return depth

code stack iteration

class Solution:
    def maxDepth(self, root):
        stack = []
        if root:
            stack.append((1, root))
        
        depth = 0
        while stack:
            current_depth, root = stack.pop()
            if root:
                depth = max(depth, current_depth)
                stack.append((current_depth + 1, root.left))
                stack.append((current_depth + 1, root.right))
        
        return depth