Leetcode 2207. Maximize Number of Subsequences in a String

Given a text and a length-2 pattern, you may insert either pattern[0] or pattern[1] exactly once anywhere; maximize how many times the pattern appears as a subsequence afterward. The task reduces to counting pattern[0]-before-pattern[1] pairs and choosing the optimal insertion (with a special case when the two pattern characters are identical, where combinations of identical letters determine the result).