Related Articles

# Generate all binary strings from given pattern

• Difficulty Level : Medium
• Last Updated : 09 Jun, 2021

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```

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 with ‘0’ or ‘1’ and recurse for remaining characters. We print the string if we reach 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 ``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

 ``

## Javascript

 ``
Output:
```10000101
10001101
10100101
10101101
11000101
11001101
11100101
11101101```

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 ``#include ``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 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:
```10000101
10001101
10100101
10101101
11000101
11001101
11100101
11101101```

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']`