java二叉树的层序遍历

落日映苍穹つ 2024-03-16 11:07 35阅读 0赞

## 二叉树的层序遍历的实现 ##

### 问题描述 ###

给你二叉树的根节点 root ，返回其节点值的 层序遍历 。 （即逐层地，从左到右访问所有节点）。

### 示例 ###

![在这里插入图片描述][f03eb1c7b3ea4aa7837eac3deb267091.png]  
![在这里插入图片描述][b5200650bb7742c8be99618760aba6da.png]

### 原题OJ链接 ###

https://leetcode.cn/problems/binary-tree-level-order-traversal/

### 解答代码 ###

/**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode() {}
     *     TreeNode(int val) { this.val = val; }
     *     TreeNode(int val, TreeNode left, TreeNode right) {
     *         this.val = val;
     *         this.left = left;
     *         this.right = right;
     *     }
     * }
     */
    import java.util.List;
    class Solution {
        
        public List<List<Integer>> levelOrder(TreeNode root) {
        
            Deque<TreeNode> deque = new LinkedList<>();
            List<List<Integer>> list2 = new LinkedList<>();
            if(root == null){
        
                return list2;
            }
            deque.offer(root);
           
            while(!deque.isEmpty()){
        
                int size = deque.size();
                List<Integer> list1 = new LinkedList<>();
                while( size>0){
        
                    TreeNode node = deque.poll();
                    size--;
                    list1.add(node.val);
                    if(node.left != null){
        
                        deque.offer(node.left);
                    }
                    if(node.right != null){
        
                        deque.offer(node.right);
                    }
                }
                list2.add(list1);               
            } 
            return list2;
        }
    }

[f03eb1c7b3ea4aa7837eac3deb267091.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/14d2e926b03f42c489c47bc0325c7701.png
[b5200650bb7742c8be99618760aba6da.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/16/3f5e99369a624a1d8921e8eaa482d4cc.png