判断二叉树是不是完全二叉树

/**
   * 完全二叉树：要么是满二叉树，要么是在满二叉树的基础上，最后一层的节点是从左到右是依次添加的
   * 采用按层遍历的方式判断是不是完全二叉树
 */
public class IsCompleteTree {

    public static void main(String[] args) {
        Node head = new Node(1);
        head.left = new Node(2);
        head.right = new Node(3);
        head.left.left = new Node(4);
        head.left.right = new Node(5);
        head.right.right = new Node(6);
        System.out.println(isCompleteTree(head));
    }

    public static boolean isCompleteTree(Node head) {
        if (head == null) {
            return true;
        }
        LinkedList<Node> queue = new LinkedList<Node>();
        queue.offer(head);
        Node left = null;
        Node right = null;
        boolean leaf = false;
        while (!queue.isEmpty()) {
            Node node = queue.poll();
            left = node.left;
            right = node.right;
            // 左节点为空，右节点不为空
            if (left == null && right != null) {
                return false;
            }
            // 当检查叶子节点状态开启时，但是又不是叶子节点时
            if (leaf && (left != null || right != null)) {
                return false;
            }
            // 开启检查叶子节点状态
            if ((left == null && right == null) || (left != null && right == null)) {
                leaf = true;
            }
            if (left != null) {
                queue.offer(left);
            }
            if (right != null) {
                queue.offer(right);
            }
        }
        return true;
    }

    public static class Node {
        Node left;
        Node right;
        int value;

        public Node(int value) {
            super();
            this.value = value;
        }
    }
}