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"]

Idea: use to_string function to trans int to string :)

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> r = vector<string>();
        if(root == NULL){
            return r;  
        }else if(root->left == NULL && root->right == NULL){
            string s = string();
            r.push_back(s + to_string(root->val));
        }else if(root->left == NULL && root->right != NULL){
            vector<string> t = binaryTreePaths(root->right);
            string s = string();
            for(int i=0;i<t.size();i++) r.push_back(s+to_string(root->val) + "->" + t[i]);
        }else if(root->left != NULL && root->right == NULL){
            vector<string> t = binaryTreePaths(root->left);
            string s = string();
            for(int i=0;i<t.size();i++) r.push_back(s+to_string(root->val) + "->" + t[i]);
        }else{
            vector<string> t = binaryTreePaths(root->right);
            string s = string();
            for(int i=0;i<t.size();i++) r.push_back(s+to_string(root->val) + "->" + t[i]);
            t = binaryTreePaths(root->left);
            for(int i=0;i<t.size();i++) r.push_back(s+to_string(root->val) + "->" + t[i]);
        }
        return r;
    }
};