Binary Tree Paths

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

Given the following binary tree:

1
/ \
2 3
\
5
All root-to-leaf paths are:

[
“1->2->5”,
“1->3”
]

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    /**     * @param root the root of the binary tree     * @return all root-to-leaf paths     */    public List<String> binaryTreePaths(TreeNode root) {        List<String> result = new ArrayList<String>();        if (root == null) {            return result;        }        helper(root, String.valueOf(root.val), result);        return result;    }    private void helper(TreeNode root, String path, List<String> result) {        if (root == null) {            return;        }        if (root.left == null && root.right == null) {            result.add(path);            return;        }        if (root.left != null) {            helper(root.left, path + "->" + String.valueOf(root.left.val), result);        }        if (root.right != null) {            helper(root.right, path + "->" + String.valueOf(root.right.val), result);        }    }}