求二叉树的深度.

public static int TreeDepth(TreeNode root) {   
        if (root==null){
            return 0;
        }
        int depth=0;
        int leftDepth = TreeDepth(root.left);
        int rightDepth=TreeDepth(root.right);
        return depth=leftDepth>rightDepth?leftDepth+1:rightDepth+1;
}