CareerCup

void printCombinations(StringBuilder s,int i){
        if(i==s.length()){
            System.out.println(s);
            return;
        }

        if(s.charAt(i)=='?'){
            s.replace(i,i+1,"0");
            printCombinations(s,i+1);
            s.replace(i,i+1,"1");
            printCombinations(s,i+1);
            s.replace(i,i+1,"?");
        }else{
            printCombinations(s,i+1);
        }
    }

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

void print_possible_combination(string input, int pos){
    if(pos >= input.size() || input.find('?', pos) == string::npos){
        cout << input << endl;
        return;
    }
    else{
        pos = input.find('?', pos);
        
        input.replace(pos, 1, "0");
        print_possible_combination(input, pos+1);
        
        input.replace(pos, 1, "1");
        print_possible_combination(input, pos+1);
    }
}

int main(){
    string input; cin >> input;
    print_possible_combination(input, 0);
}

////Sample Call

Combination("01?01", 0, "");

public static void Combination(string mainSTring, int counter, string combination_string)
        {
            if (mainSTring.Length == combination_string.Length)
            {
                System.Console.WriteLine(combination_string);
                return;
            }

            if (mainSTring[counter] == '?')
            {
                Combination(mainSTring, counter + 1, combination_string + "0");
                Combination(mainSTring, counter + 1, combination_string + "1");
                return;
            }

            Combination(mainSTring, counter + 1, combination_string + mainSTring[counter]);
        }

def allstr(str1, index, length):
    if index == length:
        print(str1)
        return
    if str1[index] == '?':
        str1[index] = 'T'
        allstr(str1, index + 1, length)
        str1[index] = 'X'
        allstr(str1, index + 1, length)
        str1[index] = '?'
    else:
        allstr(str1, index + 1, length)


t = list('he?l?o?')
allstr(t, 0, t.__len__())

Possible combinations with be nCr = n! / r! * (n - r)!
and r should be 2 here as we have only 0 or 1