Recursion-phoneKeypad.cpp

#include<iostream>
#include <vector>
using namespace std;

void solve(string digits, string output, int index, string mapping[], vector<string>& ans){
    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, mapping, ans);
        output.pop_back();
    }
}

vector<string> keyPad(string digits){
    vector<string> ans;

    if(digits.length()==0)
    return ans;

    int index= 0;
    string output= "";
    string mapping[]= {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};

    solve(digits, output, index, mapping, ans);
    return ans;
}

int main(){
    string digits;
    cout<<"enter digits"<<endl;
    cin>>digits;

    vector<string> ans = keyPad(digits);

    for(string& s : ans){
        cout<<" "<<s;
    }

    return 0;
}