vector<string> letterCombinations(string digits) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
result.clear();
letterCombinationsHelper(digits,0,"");
return result;
}
vector<string> letterCombinations(string digits) {
string pad[8] = {"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};;
vector<string> res;
string sol = "";
letterCombinationsHelper(pad, digits, 0, sol, res);
return res;
}
void letterCombinationsHelper(string pad[], string& digits, int pos, string &sol, vector<string> &res) {
if (pos == digits.size()){
res.push_back(sol);
return;
}
int idx = digits[pos] - '2';
for (int i = 0; i < pad[idx].size(); i++){
sol.push_back(pad[idx][i]);
letterCombinationsHelper(pad, digits, pos + 1, sol, res);
sol.pop_back();
}
}
void letterCombinationsHelper(string& digits, int i, string str)
{
if(i==digits.size())
{
result.push_back(str);
return;
}
int pos=digits[i]-'2';
for(int j=0; j< keypad[pos].size(); j++)
{
letterCombinationsHelper(digits,i+1,str+keypad[pos][j]);
}
}
vector<string> letterCombinations(string digits) {
if(digits.empty())
return {};
std::vector<std::string> mapping{"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
std::vector<std::string> result;
std::function<void(std::vector<std::string>&, std::string, int, std::string, vector<string>&)>
letterCombinationsHelper = [&](std::vector<string>& mapping, std::string digits, int index, std::string resStr, std::vector<string>& result)
{
if(index == digits.size())
result.push_back(resStr);
else
{
string curStr = mapping[digits[index] - '2'];
for(int i = 0, sz = curStr.size(); i < sz; ++i)
letterCombinationsHelper(mapping,digits,index + 1, resStr + curStr[i], result);
}
};
letterCombinationsHelper(mapping, digits, 0, "", result);
return result;
}
