257. Binary Tree Paths

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"]

public List<String> binaryTreePaths(TreeNode root) { List<String> res = new ArrayList<String>(); if(root!=null) helper(root, Integer.toString(root.val), res); return res; } public void helper(TreeNode root, String path, List res){ if(root.left==null&&root.right==null){ res.add(path); } if(root.left!=null){ helper(root.left, path + "->" + root.left.val, res); } if(root.right!=null){ helper(root.right, path + "->" + root.right.val, res); } }