Minimum changes to make alternating binary string https://leetcode.com/problems/minimum-changes-to-make-alternating-binary-string/description/

min.cs

public class Solution {
    public int MinOperations(string s) {
        // Using original first bit.
        int count1 = 0;
        char prev1 = s[0];
        // Using opposite first bit.
        int count2 = 1;
        char prev2 = prev1 == '0' ? '1' : '0';

        for (int i=1; i<s.Length; i++)
        {
            // Check first attempt with original first bit.
            if (prev1 == s[i])
            {
                // Flip bit.
                prev1 = prev1 == '0' ? '1' : '0';
                count1++;
            }
            else
            {
                prev1 = s[i];
            }

            // Check second attempt with first bit flipped.
            if (prev2 == s[i])
            {
                // Flip bit.
                prev2 = prev2 == '0' ? '1' : '0';
                count2++;
            }
            else
            {
                prev2 = s[i];
            }
        }

        return Math.Min(count1, count2);
    }
}

znote.txt

1758. Minimum Changes To Make Alternating Binary String
Solved
Easy
Topics
Companies
Hint
You are given a string s consisting only of the characters '0' and '1'. In one operation, you can change any '0' to '1' or vice versa.

The string is called alternating if no two adjacent characters are equal. For example, the string "010" is alternating, while the string "0100" is not.

Return the minimum number of operations needed to make s alternating.

 

Example 1:

Input: s = "0100"
Output: 1
Explanation: If you change the last character to '1', s will be "0101", which is alternating.
Example 2:

Input: s = "10"
Output: 0
Explanation: s is already alternating.
Example 3:

Input: s = "1111"
Output: 2
Explanation: You need two operations to reach "0101" or "1010".