Problem: Binary Tree Paths

class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> results = new ArrayList<>();
        List<Integer> traveler = new ArrayList<>();
        travel(traveler, results, root);

        return results;
    }

    public void travel(List<Integer> traveler, List<String> results, TreeNode root) {
        if(root == null) return;
        traveler.add(root.val);

        if(root.left == null && root.right == null) {
            results.add(convertToString(traveler));
        }
        else {
            travel(traveler, results, root.left);
            travel(traveler, results, root.right);
        }

        traveler.remove(traveler.size()-1);
    }

    public String convertToString(List<Integer> traveler) {
        if(traveler.size() == 0) return "";
        StringBuilder sb = new StringBuilder();
        sb.append(String.valueOf(traveler.get(0)));
        for(int i=1; i<traveler.size(); ++i) {
            sb.append("->").append(String.valueOf(traveler.get(i)));
        }

        return sb.toString();
    }
}