【剑指Offer】把二叉树打印成多行

题目

从上到下按层打印二叉树，同一层的结点按从左到右的顺序打印，每一层打印到一行。

实现

public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;
    
    public TreeNode(int val) {
        this.val = val;
    }
}

public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
    ArrayList<ArrayList<Integer>> results = new ArrayList<>();

    if (pRoot != null) {
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(pRoot);

        while (!queue.isEmpty()) {
            ArrayList<Integer> result = new ArrayList<>();
            int start = 0;
            int end = queue.size();

            while (start++ < end){
                TreeNode node = queue.poll();
                result.add(node.val);

                if (node.left != null)
                    queue.offer(node.left);

                if (node.right != null)
                    queue.offer(node.right);
            }

            results.add(result);
        }
    }

    return results;
}