public boolean isCompleteTree2(Node root){
        if(root == null){
            return true;
        }
        Queue<Node> queue = new LinkedList<>();
        queue.offer(root);
        while(true) {
            Node top = queue.poll();
            if (top == null) {
                while(!queue.isEmpty()) {
                    if(queue.poll() != null){
                        return false;
                    }
                }
                return true;
            } else {
                queue.offer(top.left);
                queue.offer(top.right);
            }
        }
    }

平衡二叉树

每个节点的左树和右树的高度差<=1
如果一棵树为平衡二叉树，那么这棵树的每棵子树都是平衡二叉树

判断平衡二叉树

1. 获取根节点左树的高度，及右树的高度，就算绝对值，如果结果>1,毫不客气直接返回false；如果结果<=1，说明此节点是平衡的
2. 继续判断根的左树和右数

    public int Hight(Node root){
        if(root == null){
            return 0;
        }
        int left = Hight(root.left);
        int right = Hight(root.right);
        return ((left > right) ? left : right) +1;
    }
    public boolean isBalanced(Node root){
        if(root == null){
            return true;
        }
        int leftHight = Hight(root.left);
        int rightHIght = Hight(root.right);
        if(Math.abs(leftHight - rightHIght) >1 ){
            return false;
        }
        return isBalanced(root.left) && isBalanced(root.right);
    }

    public int Hight(Node root){
        if(root == null){
            return 0;
        }
        int leftHight = Hight(root.left);
        int rightHight = Hight(root.right);
        if(leftHight == -1 || rightHight == -1 || Math.abs(leftHight - rightHight) > 1){
            return -1;
        }
        return (leftHight > rightHight ? leftHight : rightHight) + 1;
    }
    public boolean isBalanced(Node root){
        if(Hight(root) != -1){
            return true;
        }
        return false;
    }

    public boolean isSymmeticChild(Node leftroot , Node rightroot){
        if(leftroot == null && rightroot == null){
            return true;
        }
        if(leftroot == null || rightroot == null){
            return false;
        }
        if(leftroot.getVal() != rightroot.getVal()){
            return false;
        }
        return isSymmeticChild(leftroot.right , rightroot.left) && isSymmeticChild(leftroot.left , rightroot.right);
    }
    public boolean isSymmetric(Node root){
        if(root == null){
            return true;
        }
        return isSymmeticChild(root.left,root.right);
    }

    public Node Mirror (Node root){
        if(root == null){
            return root;
        }
        if(root.left == null && root.right == null){
            return root;
        }
        Node temp = root.left;
        root.left = root.right;
        root.right = temp;
        root.left = Mirror(root.left);
        root.left = Mirror(root.right);
        return root;
    }