面试题32 - I. 从上到下打印二叉树

我不是女神ヾ 2023-02-11 08:52 12阅读 0赞

# 题目： #

[面试题32 - I. 从上到下打印二叉树][32 - I.]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70]

# 题解： #

![在这里插入图片描述][20200522163538555.png]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 2]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 3]

# 代码： #

import java.util.*;
    
    public class 面试题32 { 
    
        public static int[] levelOrder(TreeNode root) { 
            if(root == null)
            { 
                int temp[] = new int[0];
                return temp;
            }
            Queue<TreeNode> queue = new LinkedList<>();
            List<Integer> list = new ArrayList<>();
            queue.offer(root);
            while(!queue.isEmpty())
            { 
                TreeNode node = queue.poll();
                list.add(node.val);
                if(node.left != null)
                { 
                    queue.offer(node.left);
                }
                if(node.right != null)
                { 
                    queue.offer(node.right);
                }
            }
            int res[] = new int[list.size()];
            for(int i = 0; i < list.size(); i++)
            { 
                res[i] = list.get(i);
            }
            return res;
        }
        
        public static void main(String[] args) { 
            System.out.println("***************************************");
            Integer nums[] = {  3, 9, 20, null, null, 15, 7 };
            TreeNode root = ConstructTree.constructTree(nums);
            TreeOperation.show(root);
            System.out.println("***************************************");
            int res[] = levelOrder(root);
            for(int i = 0; i < res.length; i++)
            { 
                System.out.print(res[i] + " ");
            }
            System.out.println();
        }
    }

# 参考： #

1.  [面试题32 - I. 从上到下打印二叉树（层序遍历 BFS ，清晰图解）][32 - I. _ BFS]

[32 - I.]: https://leetcode-cn.com/problems/cong-shang-dao-xia-da-yin-er-cha-shu-lcof/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200522163412738.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ==,size_16,color_FFFFFF,t_70
[20200522163538555.png]: https://img-blog.csdnimg.cn/20200522163538555.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200522163554708.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20200522163646661.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ==,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/20200522163716645.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ==,size_16,color_FFFFFF,t_70
[32 - I. _ BFS]: https://leetcode-cn.com/problems/cong-shang-dao-xia-da-yin-er-cha-shu-lcof/solution/mian-shi-ti-32-i-cong-shang-dao-xia-da-yin-er-ch-4/