/**

public boolean isSubtree(TreeNode s, TreeNode t) {

return isEqual(s, t) || (s != null && (isSubtree(s.left, t) || isSubtree(s.right, t)));

}

private boolean isEqual(TreeNode s, TreeNode t) {

if (t == null && s == null) {

return true;

}

if (t == null || s == null) {

return false;

}

return s.val == t.val && isEqual(s.left, t.left) && isEqual(s.right, t.right);

}