leetcode -Maximum Depth of Binary Tree

question:

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.

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 Tree Depth-first Search

answer:

遞歸法：

/**
 * Definition for binary tree
 * 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;
        }
        int left=maxDepth(root.left);
        int right=maxDepth(root.right);
        return Math.max(left,right)+1;
    }
}