实不相瞒，我笑了

就是这样：

/**
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) {
        return root==null?0:Math.max(TreeDepth(root.left),TreeDepth(root.right))+1;
    }
}