import java.util.*;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public int TreeDepth(TreeNode root) {
        if(root==null){
            return 0;
        }
        int high_left=TreeDepth(root.left);
        int high_right=TreeDepth(root.right);
        return 1+Math.max(high_left,high_right);
    }
}

以前完全写不出来的东西,现在也写出来了。