[LeetCode] 104. Maximum Depth of Binary Tree

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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.

Note: A leaf is a node with no children.

Example:

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

Explanation

  1. We want to find the maximum height of the tree, which means we need to find the height of the left subtree plus one and the height of the right subtree plus one. Compare both and take the maximum.

  2. The base case is if the root tree node is NULL, we return 0.

Solution

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/**
 * 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;
        return 1+Math.max(maxDepth(root.left), maxDepth(root.right));
    }
}