二叉树的所有路径

给你一个二叉树的根节点 root ，按 任意顺序 ，返回所有从根节点到叶子节点的路径。

叶子节点 是指没有子节点的节点。

示例 1：

输入：root = [1,2,3,null,5]
输出：["1->2->5","1->3"]

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;*     }* }*/
class Solution {List<String> res = new ArrayList<>();public List<String> binaryTreePaths(TreeNode root) {if(root ==null) {return res;}dfs(root,root.val+"");return res;}public void dfs(TreeNode root,String path) {if (root.left == null && root.right == null ) {res.add(path);return;}if(root.left != null) {dfs(root.left,path+ "->" + root.left.val);}if(root.right != null) {dfs(root.right,path+ "->" + root.right.val);}}
}