Minimum Changes Required for Alternating Binary String in Python

Suppose we have a binary string s. Let us consider an operation where we can flip one bit. The string s is called alternating string if no two adjacent characters are same. We have to find the minimum number of operations needed to make s alternating.

So, if the input is like s = "11100011", then the output will be 3 because if we flip bits at position 1, 4 and 7, then, it will be "10101010", then all are alternating.

To solve this, we will follow these steps −

• change := 0

• even_1 := 0, even_0 := 0

• odd_1 := 0, odd_0 := 0

• for i in range 0 to size of s - 1, do

  • if i is even, then

    • if s[i] is same as '1', then

      • even_1 := even_1 + 1

    • otherwise,

      • even_0 := even_0 + 1

  • otherwise,

    • if s[i] is same as '1', then

      • odd_1 := odd_1 + 1

    • otherwise,

      • odd_0 := odd_0 + 1

• if (even_1+odd_0) > (even_0+odd_1), then

  • change := even_0 + odd_1

• otherwise,

  • change := even_1 + odd_0

• return change

Example (Python)

Let us see the following implementation to get better understanding &minnus;

 Live Demo

def solve(s):
   change = 0
   even_1 = 0
   even_0 = 0
   odd_1 = 0
   odd_0 = 0
   for i in range(len(s)):
      if(i%2 == 0):
         if(s[i]=='1'):
            even_1 +=1
         else:
            even_0 +=1
      else:
         if(s[i] == '1'):
            odd_1 +=1
         else:
            odd_0 +=1
   if((even_1+odd_0)>(even_0+odd_1)):
      change = even_0 + odd_1
   else:
      change = even_1 + odd_0
   return change

s = "11100011"
print(solve(s))

Input

"11100011"

Output

3