104 Maximum Depth of Binary Tree – Easy¶

Problem:¶

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.

Thoughts:¶

Very straight forward with recursion.

Solutions:¶

Iterative way:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        Queue<TreeNode> q = new LinkedList<TreeNode>();
        q.add(root);
        int count = 0;
        while (q.size() > 0) {
            int n = q.size();
            count++;
            for (int i = 0; i < n; i ++) {
                TreeNode node = q.remove();
                if (node.left != null) {
                    q.add(node.left);
                }
                if (node.right !=null) {
                    q.add(node.right);
                }
            }
        }
        return count;
    }
}

Recursion way:

public class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
    }
}