#257二叉树的所有路径

import java.util.*;

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int val) {
        this.val = val;
    }
}

class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> result = new ArrayList<>();
        if (root != null) dfs(root, "", result);
        return result;
    }

    private void dfs(TreeNode node, String prefix, List<String> result) {
        String path = prefix.isEmpty() ? Integer.toString(node.val)
                : prefix + "->" + node.val;
        if (node.left == null && node.right == null) {
            result.add(path);
            return;
        }
        if (node.left != null) dfs(node.left, path, result);
        if (node.right != null) dfs(node.right, path, result);
    }
}