# Program to find 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