[leetcode]104. Maximum Depth of Binary Tree二叉树最大深度

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.

 

题意：

求二叉树最大深度

 

Solution1： DFS

 

code

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