Number of Flips to Make Binary String Alternate in C++

Let's say you have given a binary string "10011". To make an alternate binary string, we need to flip a minimum of 2 characters as "10101".

There are two possibilities for the alternate string. It will start with 0 or 1. We will check for two alternates and count the number of flips required for both.

And then return the minimum of both. Let's see an example.

Input

binary = "10011"

Output

2

If we start the string with 0, then we have to flip 3 times. And if we start the string with 1, then we have to flip 2 times. The minimum is 2.

Algorithm

• Initialise the binary string.
• Count the flips required to make string alternate starting with 1.
• Similarly count the flips required to make string alternate starting with 0.
• Find the minimum from the above two.
• Print the menimum.

Implementation

Following is the implementation of the above algorithm in C++

#include <bits/stdc++.h>
using namespace std;
char flip(char binaryDigit) {
   return binaryDigit == '0' ? '1' : '0';
}
int getFlipCountToAlternateString(string binary, char expected) {
   int flipCount = 0;
   for (int i = 0; i < binary.length(); i++) {
      if (binary[i] != expected) {
         flipCount++;
      }
      expected = flip(expected);
   }
   return flipCount;
}
int main() {
   string binary = "10011";
   cout << min(getFlipCountToAlternateString(binary, '0'), getFlipCountToAlternateString(binary,       '1')) << endl;
   return 0;
}

Output

If you run the above code, then you will get the following result.

2