​LeetCode刷题实战257：二叉树的所有路径

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public  List<String> binaryTreePaths(TreeNode root) {
        List<String> list = new LinkedList<>();
        helper(root, "", list);
        return list;
    }
    
    private void helper(TreeNode root, String s, List<String>list){
        if (root == null){
            return;
        }
        
        s = s + root.val;
        
        if (root.left == null && root.right == null){
            list.add(s);
            return;
        }
        
        if (root.left != null){
            helper(root.left, s + "->", list);
        }

        if (root.right != null){
            helper(root.right, s + "->", list);
        }
    }
 
    
 
}