}
		//@return: return next node
		public TreeNode next() {
			// write your code here
			TreeNode rel=null;
			while (c!=null) {
				if (c.left!=null) {
					TreeNode t=c.left;
					while (t.right!=c&&t.right!=null)
						t=t.right;
					if (t.right==c) {
						t.right=null;
						rel=c;
						c=c.right;
						break;
					} else {
						t.right=c;
						c=c.left;
					}
				} else {
					rel=c;
					c=c.right;
					break;
				}
			}