Generate binary string
Easy Accuracy: 64.99% Submissions: 1031 Points: 2

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

Example 1:

Input: 1??0?101
Output: 10000101 10001101 10100101 10101101
11000101 11001101 11100101 11101101
Explanation:
There will be 8 such possible strings that
can be formed, they are 10000101, 10001101,
10100101, 10101101, 11000101, 11001101,
11100101 and 11101101.


Example 2:

Input: 10?
Output: 100 101
Explanation: There are 2 such possible strings
and they are 100 and 101.


You don't need to read or print anything. Your task is to complete the function generate_binary_string() which takes the given string as input parameter and returns a vector of strings containing all the possible strings that can be formed.

Expected Time complexity: O(2n)
Expected Space complexity: O(n*2n)

Constraints:
1 ≤ length of string ≤ 30

Note: Number of '?' in any string does not exceed 15.

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