LeetCode 104. Maximum Depth of Binary Tree

Description

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.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return its depth = 3.Accepted

Explanation

List all scenarios of what a binary tree could be like:

1. when a binary tree is null, simply return maximum depth as 0
2. when a binary tree just have a root node, return maximum depth as 1
3. when a binary tree has a root node and child nodes, maximum depth would be the depth of the bigger side between left and right subtrees plus 1.

Java Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        
        int leftDepth = maxDepth(root.left);
        int rightDepth = maxDepth(root.right);
        
        return Math.max(leftDepth, rightDepth) + 1;
    }
}

Python Solution

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

class Solution:
    def maxDepth(self, root: TreeNode) -> int:
        if root == None:
            return 0
        
        left = self.maxDepth(root.left)
        right = self.maxDepth(root.right)
        
        max_depth = max(left, right) + 1
        
        return max_depth
        

• Time Complexity: O(N)
• Space Complexity: O(log(N))