[LeetCode] 17 - Letter Combinations of a Phone Number

class Solution 
{
    map<char,string> digitComb
    {
        {'2', "abc"},
        {'3', "def"},
        {'4', "ghi"},
        {'5', "jkl"},
        {'6', "mno"},
        {'7', "pqrs"},
        {'8', "tuv"},
        {'9', "wxyz"}
    };

    vector<string> res;
    string digits;

public:
    void DFS(int i = 0, string curStr = "")
    {
	    if (curStr.size() == digits.size())
	    {
		    res.push_back(curStr);
		    return;
	    }
	    for (auto& c : digitComb[digits[i]])
		    DFS(i + 1, curStr + c);
    }

    vector<string> letterCombinations(string digits)
    {
        this->digits = digits;
        
	    if (digits.size())
		    DFS();

	    return res;
    }
};