phone_keyword.cpp

//Letter Combinations of a Phone Number
// codelink :: https://leetcode.com/problems/letter-combinations-of-a-phone-number/
/*for ex - 
    i/p : 23
    o/p : ad,ae,af,bd,be,bf,cd,ce,cf
*/
#include<iostream>
#include<vector>
using namespace std;

void solve(string digits, string output, int index, vector<string> &ans,string mapping[]){
    //base case
    if (index>=digits.length()){
    ans.push_back(output);
    return;
    }
    int number = digits[index] - '0';
    string value = mapping[number];
    for(int i =0;i<value.length();i++){
        output.push_back(value[i]);
        solve(digits,output,index+1,ans,mapping);
        output.pop_back();
    }
}

vector<string> letterCombinations(string digits) {
    vector<string> ans;
    if(digits.length() == 0){
        return ans;
    }
    string output = "";
    int index = 0;
    string mapping[10] = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
    solve(digits,output,index,ans,mapping);
    return ans;
}

int main(){
    string s;
    cin >> s;
    vector<string> ans = letterCombinations(s);
    for(int i=0;i<ans.size();i++){
        cout << ans[i] <<", ";
    }
    return 0;
}