1758 Minimum Changes To Make Alternating Binary String - Easy

Problem:

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".

Constraints:

• 1 <= s.length <= 104
• s[i] is either '0' or '1'.

Problem Analysis:

The goal of this solution is to find the minimum number of operations needed to make a binary string (consisting of '0' and '1') either all '0's or all '1's. An operation involves flipping a consecutive subarray of characters. The strategy is to iterate through the string and count the operations needed for two possible starting points: starting with '0' and starting with '1'. The final result is the minimum of these two counts.

Complexity:

• Time Complexity: O(n), where n is the length of the input string s. The solution iterates through the string once.
• Space Complexity: O(1). The algorithm uses a constant amount of space for the count variable.

Solutions:

class Solution:
    def minOperations(self, s: str) -> int:
        count = 0 # operations start w 0

        for i in range(len(s)):
            if i%2:
                count += 1 if s[i] != "0" else 0
            else:
                count += 1 if s[i] != "1" else 0
        # len(s) - count: operations start w 1
        return min(count, len(s) - count)

Similar Questions