#104 Maximum Depth of Binary Tree

Description

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.

Examples

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

思路

dfs

代码

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