Generate all binary strings from given pattern

Given a string containing of ‘0’, ‘1’ and ‘?’ wildcard characters, generate all binary strings that can be formed by replacing each wildcard character by ‘0’ or ‘1’.
Example :

Input str = "1??0?101"
Output: 
        10000101
        10001101
        10100101
        10101101
        11000101
        11001101
        11100101
        11101101

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Method 1 (Using Recursion)
We pass index of next character to the recursive function. If the current character is a wildcard character ‘?’, we replace it by ‘0’ or ‘1’ and recurse for remaining characters. We print the string if we reaches its end.

Below is recursive the implementation.

C++

// Recursive C++ program to generate all binary strings 
// formed by replacing each wildcard character by 0 or 1 
#include <iostream> 
using namespace std; 
  
// Recursive function to generate all binary strings 
// formed by replacing each wildcard character by 0 or 1 
void print(string str, int index) 
{ 
    if (index == str.size()) 
    { 
        cout << str << endl; 
        return; 
    } 
  
    if (str[index] == '?') 
    { 
        // replace '?' by '0' and recurse 
        str[index] = '0'; 
        print(str, index + 1); 
  
        // replace '?' by '1' and recurse 
        str[index] = '1'; 
        print(str, index + 1); 
  
        // No need to backtrack as string is passed 
        // by value to the function 
    } 
    else
        print(str, index + 1); 
} 
  
// Driver code to test above function 
int main() 
{ 
    string str = "1??0?101"; 
  
    print(str, 0); 
  
    return 0; 
} 

Java

// Recursive Java program to generate all  
// binary strings formed by replacing  
// each wildcard character by 0 or 1  
import java.util.*; 
import java.lang.*; 
import java.io.*; 
  
class binStr 
{    
    // Recursive function to generate all binary 
    // strings formed by replacing each wildcard 
    // character by 0 or 1  
    public static void print(char str[], int index) 
    { 
        if (index == str.length) 
        { 
            System.out.println(str); 
            return; 
        } 
  
        if (str[index] == '?') 
        { 
            // replace '?' by '0' and recurse 
            str[index] = '0'; 
            print(str, index + 1); 
              
            // replace '?' by '1' and recurse 
            str[index] = '1'; 
            print(str, index + 1); 
              
            // NOTE: Need to backtrack as string 
            // is passed by reference to the 
            // function 
            str[index] = '?'; 
        } 
        else
            print(str, index + 1); 
    } 
  
    // driver code 
    public static void main (String[] args) 
    { 
        String input = "1??0?101"; 
        char[] str = input.toCharArray(); 
        print(str, 0); 
    } 
} 
  
// This code is contributed by Chhavi 

Python3

# Recursive Python program to generate all 
# binary strings formed by replacing 
# each wildcard character by 0 or 1 
  
# Recursive function to generate all binary 
# strings formed by replacing each wildcard 
# character by 0 or 1 
def _print(string, index): 
    if index == len(string): 
        print(''.join(string)) 
        return
  
    if string[index] == "?": 
  
        # replace '?' by '0' and recurse 
        string[index] = '0'
        _print(string, index + 1) 
  
        # replace '?' by '1' and recurse 
        string[index] = '1'
        _print(string, index + 1) 
  
        # NOTE: Need to backtrack as string 
        # is passed by reference to the 
        # function 
        string[index] = '?'
    else: 
        _print(string, index + 1) 
  
# Driver code 
if __name__ == "__main__": 
  
    string = "1??0?101"
    string = list(string) 
    _print(string, 0) 
  
    # This code is contributed by 
    # sanjeev2552 
  
# Note: function name _print is used because 
# print is already a predefined function in Python 

C#

// Recursive C# program to generate all  
// binary strings formed by replacing  
// each wildcard character by 0 or 1  
using System;  
  
class GFG 
{  
    // Recursive function to generate  
    // all binary strings formed by  
    // replacing each wildcard character 
    // by 0 or 1  
    public static void print(char []str,  
                             int index) 
    { 
        if (index == str.Length) 
        { 
            Console.WriteLine(str); 
            return; 
        } 
  
        if (str[index] == '?') 
        { 
            // replace '?' by  
            // '0' and recurse 
            str[index] = '0'; 
            print(str, index + 1); 
              
            // replace '?' by  
            // '1' and recurse 
            str[index] = '1'; 
            print(str, index + 1); 
              
            // NOTE: Need to backtrack  
            // as string is passed by  
            // reference to the function 
            str[index] = '?'; 
        } 
        else
            print(str, index + 1); 
    } 
  
    // Driver Code 
    public static void Main () 
    { 
        string input = "1??0?101"; 
        char []str = input.ToCharArray(); 
        print(str, 0); 
    } 
} 
  
// This code is contributed by nitin mittal. 

PHP

<?php 
// Recursive PHP program to generate all binary strings 
// formed by replacing each wildcard character by 0 or 1 
  
// Recursive function to generate all binary strings 
// formed by replacing each wildcard character by 0 or 1 
function print1($str, $index) 
{ 
    if ($index == strlen($str)) 
    { 
        echo $str."\n"; 
        return; 
    } 
  
    if ($str[$index] == '?') 
    { 
        // replace '?' by '0' and recurse 
        $str[$index] = '0'; 
        print1($str, $index + 1); 
  
        // replace '?' by '1' and recurse 
        $str[$index] = '1'; 
        print1($str, $index + 1); 
  
        // No need to backtrack as string is passed 
        // by value to the function 
    } 
    else
        print1($str, $index + 1); 
} 
  
// Driver code 
  
    $str = "1??0?101"; 
  
    print1($str, 0); 
  
      
// This code is contributed by chandan_jnu 
?> 

Output:

Method 2 (Using Queue)
We can also achieve this by using iteration. The idea is to use queue. We find position of first occurrence of wildcard character in the input string and replace it by ‘0’ , then ‘1’ and push both strings into the queue. Then we pop next string from the queue, and repeat the process till queue is empty. If no wildcard characters are left, we simply print the string.

Iterative C++ implementation using queue.

C++

// Iterative C++ program to generate all binary 
// strings formed by replacing each wildcard 
// character by 0 or 1 
#include <iostream> 
#include <queue> 
using namespace std; 
  
// Iterative function to generate all binary strings 
// formed by replacing each wildcard character by 0 
// or 1 
void print(string str) 
{ 
    queue<string> q; 
    q.push(str); 
  
    while (!q.empty()) 
    { 
        string str = q.front(); 
  
        // find position of first occurrence of wildcard 
        size_t index = str.find('?'); 
  
        // If no matches were found, 
        // find returns string::npos 
        if(index != string::npos) 
        { 
            // replace '?' by '0' and push string into queue 
            str[index] = '0'; 
            q.push(str); 
  
            // replace '?' by '1' and push string into queue 
            str[index] = '1'; 
            q.push(str); 
        } 
  
        else
            // If no wildcard characters are left, 
            // print the string. 
            cout << str << endl; 
  
        q.pop(); 
    } 
} 
  
// Driver code to test above function 
int main() 
{ 
    string str = "1??0?101"; 
  
    print(str); 
  
    return 0; 
} 

Output:

Method 3 (Using str and Recursion)

Python3

#we store processed strings in all (array) 
#we see if string as "?", if so, replace it with 0 and 1 
#and send it back to recursive func until base case is reached 
#which is no wildcard left 
  
res = [] 
def genBin(s): 
    if '?' in s: 
        s1 = s.replace('?','0',1) #only replace once 
        s2 = s.replace('?','1',1) #only replace once 
        genBin(s1) 
        genBin(s2) 
    else: res.append(s) 
  
# Driver code 
genBin("1??0?101") 
print(res) 
  
# This code is contributed by 
# divay pandey 

Output:

['10000101', '10001101', '10100101', '10101101', '11000101', '11001101', '11100101', '11101101']

This article is contributed by Aditya Goel. If you like GeeksforGeeks and would like to contribute, you can also write an article and mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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My Personal Notes

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

C++

Java

Python3

C#

PHP

C++

Python3

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