剑指offer 32 - II. 从上到下打印二叉树 II

剑指offer 32 - II. 从上到下打印二叉树 II

题目描述

解题思路

class Solution {
    
    
    public List<List<Integer>> levelOrder(TreeNode root) {
    
    
        List<List<Integer>> res = new ArrayList<>();

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

        while (!queue.isEmpty()) {
    
    
            //保存当前层的节点
            List<Integer> temp = new ArrayList<>();
            int size = queue.size();
            for (int i = 0; i < size; i++) {
    
    
                TreeNode currNode = queue.poll();
                //保存结果
                temp.add(currNode.val);
                //左右孩子入队
                if (currNode.left != null) queue.offer(currNode.left);
                if (currNode.right != null) queue.offer(currNode.right);
            }
            res.add(temp);  
        }
        return res;
    }
}