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.

Constraints

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

Example 1

Input: [3, 9, 20, null, null, 15, 7]

Output: 3

Solutions

TreeNode

// Definition for a binary tree node.
public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    
    TreeNode() {}
    
    TreeNode(int val) { this.val = val; }
    
    TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

Solution 1

/**
 * Time complexity : O(N)
 * Space complexity : O(log(N))
 */

class Solution {
    public int maxDepth(TreeNode root) {
        int depth = 0;
        if(root == null) return depth;
        Queue<TreeNode> queue = new LinkedList();
        queue.add(root);
        while(!queue.isEmpty()) {
            depth++;
            int noOfNodes = queue.size();
            for(int i = 0; i < noOfNodes; i++) {
                TreeNode node = queue.poll();
                if(node.left != null) {
                    queue.add(node.left);
                }
                if(node.right != null) {
                    queue.add(node.right);
                }
            }
        }
        return depth;
    }
}

Solution 2

/**
 * Time complexity : O(N)
 * Space complexity : O(log(N))
 */

class Solution {
    public int maxDepth(TreeNode root) {
        if(root == null) return 0;
        int leftDepth = 1 + maxDepth(root.left);
        int rightDepth = 1 + maxDepth(root.right);
        return (leftDepth > rightDepth)? leftDepth: rightDepth;
    }
}

Follow up

• Sum of nodes at maximum depth of a Binary Tree - GFG