Leetcode 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"]

 解法: 继续用深度搜索的方法。注意这里的递归过程，各自数据结构之间的转换。

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