刷题 | leetcode 102. 二叉树的层序遍历

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 1：

解题思路：

二叉树的广度优先遍历，就是java和python来回切换我这个语法有点混了

/**
 * 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;
 *     }
 * }
 */
class Solution {
     HashMap> nodemap = new HashMap>();
    public List> levelOrder(TreeNode root) {
        List> result = new ArrayList>();
        int level = 0;
        recurr(root, level);
        for(int i = 0; i < nodemap.size(); i++){
            result.add(nodemap.get(i));
        }
        return result;
    }
   
    public void recurr(TreeNode node, int level){
        if(node == null){
            return;
        }
        if(nodemap.containsKey(level)){
            List tem = new ArrayList();
            tem = nodemap.get(level);
            tem.add(node.val);
            nodemap.put(level,tem);
        }else{
            List tem = new ArrayList();
            tem.add(node.val);
            nodemap.put(level,tem);
        }

        recurr(node.left, level + 1);
        recurr(node.right, level + 1);

    }

}