Minimum Number of Flips to Make the Binary String Alternating - Solution & Explanation

One efficient approach is to use a sliding window to determine the number of flips required for each substring of length equal to the original string.

For a binary string to be alternating, it can follow two patterns: '010101...' (starting with '0') and '101010...' (starting with '1'). We can employ a combination of the two permitted operations: character removal and appending, and character flipping, to transform the string into one of those patterns with the minimum number of flips.

This solution attempts both alternating patterns using a sliding window over a string doubled to simulate rotations. It counts mismatches for both patterns, adjusting counts when the window slides.

Another approach is to use a greedy strategy based on calculating mismatches directly without explicitly considering rotations. This involves calculating mismatches for two possible alternating patterns from the start and adjusting for the effect of rotations. This can be achieved by maintaining two mismatch counters for the two patterns and adjusting them based on the original string and its windowed variants.

This greedy approach initializes mismatch counts for both patterns. It calculates these mismatches over the length of the input string and then chooses the minimum of both as the answer.