[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”]
Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

这种第一时间想到的就是递归啦。考虑好结束条件，就是左右子树都为空即叶子节点为结束条件，依次递归，不过要考虑好字符串的处理问题。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class