Binary Tree Paths

BinaryTreePaths.java

package com.interviewbytes.trees;

import java.util.ArrayList;
import java.util.List;

public class BinaryTreePaths {

    public List<String> binaryTreePaths(TreeNode root) {

        List<String> paths = new ArrayList<>();

        helper(root, "", paths);

        return paths;

    }

    private void helper(TreeNode node, String path, List<String> paths) {
        if (node == null) return;

        path += path.isEmpty() ? node.val : "->" + node.val;

        if (node.left == null && node.right == null) paths.add(path);

        helper(node.left, path, paths);
        helper(node.right, path, paths);
    }
}

TreeNode.java

package com.interviewbytes.trees;

public class TreeNode {

    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}