剑指 Offer 32 - I. 从上到下打印二叉树

今天药忘吃喽~ 2022-12-23 11:18 115阅读 0赞

# 题目来源 #

[剑指 Offer 32 - I. 从上到下打印二叉树][Offer 32 - I.]

# 题目描述 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70_pic_center]

# 题目解析 #

层次遍历

/**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    class Solution {
        
    public int[] levelOrder(TreeNode root) {
        
            if (root == null){
        
                return new int[0];
            }
    
            List<Integer> list = new LinkedList<>();
            Queue<TreeNode> queue = new LinkedList<>();
            queue.offer(root);
            while (!queue.isEmpty()){
        
                int size = queue.size();
                for (int i = 0; i < size; i++){
        
                    TreeNode pop = queue.poll();
                    list.add(pop.val);
                    if (pop.left != null){
        
                        queue.offer(pop.left);
                    }
                    if (pop.right != null){
        
                        queue.offer(pop.right);
                    }
                }
            }
    
            int [] ints = new int[list.size()];
            for (int i = 0; i < list.size(); i++){
        
                ints[i] = list.get(i);
            }
            return ints;
        }
    }

[Offer 32 - I.]: https://leetcode-cn.com/problems/cong-shang-dao-xia-da-yin-er-cha-shu-lcof/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70_pic_center]: /images/20221120/24d7ae68ad09483fbfbeffa58bd06705.png