Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

   1
 /   \
2     3
 \
  5

All root-to-leaf paths are:

["1-
>
2-
>
5", "1-
>
3"]

Credits:
Special thanks to@jianchao.li.fighterfor adding this problem and creating all test cases.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private class Node{
        TreeNode nd;
        String path;

        public Node(TreeNode nd, String path){
            this.nd = nd;
            this.path = path;
        }
    }

    public List<String> binaryTreePaths(TreeNode root) {
        List<String> ans = new ArrayList<>();
        if (root == null) return ans;

        Queue<Node> q = new LinkedList<>();
        q.offer(new Node(root, root.val + ""));

        while (!q.isEmpty()){
            Node cur = q.poll();
            if (cur.nd.left == null && cur.nd.right == null){
                ans.add(cur.path);
            }

            if (cur.nd.left != null){
                q.offer(new Node(cur.nd.left, cur.path + "->" + cur.nd.left.val));
            }

            if (cur.nd.right != null){
                q.offer(new Node(cur.nd.right, cur.path + "->" + cur.nd.right.val));
            }
        }

        return ans;
    }
}