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AC代码：

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    /**     * @param root: The root of binary tree.     * @return: An integer.     */    public int maxDepth(TreeNode root) {        if(root==null) return 0;        return Math.max(maxDepth(root.left),maxDepth(root.right))+1;    }}

 

题目来源：