class Solution {
public:
void solve(vector<vector >&v,vector&ans,string digits,int pos,string s)
{
if(pos==digits.size())
{
if(s!="")
ans.push_back(s);return;
}
int temp=digits[pos]-'0';
for(int i=0;i<v[temp].size();i++)
{
s.push_back(v[temp][i]);
solve(v,ans,digits,pos+1,s);
s.pop_back();
}
}
vector letterCombinations(string digits) {
string s;
vector<vector > v{{},{},{'a','b','c'},{'d','e','f'},{'g','h','i'},{'j','k','l'},
{'m','n','o'},{'p','q','r','s'},{'t','u','v'},{'w','x','y','z'}};
vector ans;
solve(v,ans,digits,0,"");
return ans;
}
};