剑指 Offer 32 - II. 分行从上到下打印二叉树 II

题目描述

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

解题思路

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {

        List<List<Integer>> res = new ArrayList<>();
        if(root == null) return res;

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

        while(!queue.isEmpty()){
            int size = queue.size();
            List<Integer> list = new ArrayList<>();
            for(int i = 0; i < size; i++){
                TreeNode node = queue.poll();
                list.add(node.val);

                if(node.left != null)
                    queue.add(node.left);
                if(node.right != null)
                    queue.add(node.right);
            }
            res.add(list);
        }
        return res;
    }
}