二叉树层序遍历 java

层序遍历

1.把根结点放到队列中

2.循环直到？

      1.从队列取出队首元素  2.孩子入队列

​public static void levelOrder1(TreeNode root) {
        if (root == null) {
            return;
        }

        Queue queue = new LinkedList<>();
        queue.add(root);

        while (!queue.isEmpty()) {
            TreeNode front = queue.poll();
            System.out.println(front.val);
            if (front.left != null) {
                queue.add(front.left);
            }
            if (front.right != null) {
                queue.add(front.right);
            }
        }
    }
​