Leetcode 3298. Count Substrings That Can Be Rearranged to Contain a String II

Count the substrings of word1 that can be rearranged so word2 appears as a prefix — equivalently, substrings of length >= |word2| whose character-count vector component-wise dominates that of word2. Because word1 can be very long, this must be done in linear time with small extra memory (fixed 26-letter alphabet), typically using a sliding-window / frequency-difference approach.