import java.util.LinkedList;

import java.util.List;

public class BinaryTreePaths {

// 耗时2ms

public List<String> binaryTreePaths(TreeNode root) {

List<String> list = new LinkedList<>();

if (root == null) {

return list;

}

helper(root, list, "");

return list;

}

private void helper(TreeNode root, List<String> list, String path) {

if (root == null) {

return;

}

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

if (root.left == null && root.right == null) {

list.add(path);

return;

}

helper(root.left, list, path);

helper(root.right, list, path);

}

}