Number of flips to make binary string alternate | Set 1

Given a binary string, that is it contains only 0s and 1s. We need to make this string a sequence of alternate characters by flipping some of the bits, our goal is to minimize the number of bits to be flipped. 

Examples : 

Input : str = “001”
Output : 1
Minimum number of flips required = 1
We can flip 1st bit from 0 to 1 

Input : str = “0001010111”
Output : 2
Minimum number of flips required = 2
We can flip 2nd bit from 0 to 1 and 9th 
bit from 1 to 0 to make alternate 
string “0101010101”.

Expected time complexity : O(n) where n is length of input string.

We can solve this problem by considering all possible results, As we are supposed to get alternate string, there are only 2 possibilities, alternate string starting with 0 and alternate string starting with 1. We will try both cases and choose the string which will require minimum number of flips as our final answer. 

Trying a case requires O(n) time in which we will loop over all characters of given string, if current character is expected character according to alternation then we will do nothing otherwise we will increase flip count by 1. After trying strings starting with 0 and starting with 1, we will choose the string with minimum flip count. 

Total time complexity of solution will be O(n) 

Implementation:

2

Time Complexity: O(N)
Auxiliary Space: O(1) 

Minimum number of replacements to make the binary string alternating | Set 2