LeetCode || Binary Tree Paths

/**
* 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<int> curr;

string ChangInt2String(const vector<int>& v)
{
string s;
if(v.size()== 0)
return s;
char str[5];
sprintf(str, "%d", v[0]);
s+=str;
for(int i = 1;i<v.size();i++)
{
sprintf(str, "->%d", v[i]);
s+=str;
}
return s;
}
void dfs(TreeNode* root, vector<string>& paths)
{
if(root->left == NULL && root->right == NULL)
{
string t = ChangInt2String(curr);
paths.push_back(t);
return;
}

if(root->left != NULL)
{
curr.push_back(root->left->val);
dfs(root->left, paths);
curr.pop_back();
}

if(root->right != NULL)
{
curr.push_back(root->right->val);
dfs(root->right, paths);
curr.pop_back();
}
}
vector<string> binaryTreePaths(TreeNode* root) {
vector<string> paths;
if(root == NULL)
return paths;
curr.push_back(root->val);
dfs(root, paths);
return paths;
}
};