根据两种遍历确定二叉树(树的后序遍历等价于该树对应二叉树的)

	public static Queue bfs(TreeNode root){
        Queue queue=new linkedList<>();
        Queue help=new linkedList<>();
        help.offer(root);
        while (!help.isEmpty()){
            TreeNode poll = help.poll();
            queue.offer(poll.val);
            if(poll.left!=null) help.offer(poll.left);
            if(poll.right!=null) help.offer(poll.right);
        }
        return queue;
    }

	public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode() {
        }
        TreeNode(int val) {
            this.val = val;
        }
        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }