Leetcode 411. Minimum Unique Word Abbreviation

Given a target word and a dictionary, find the shortest abbreviation (letters kept + counts for omitted runs) of the target that cannot represent any dictionary word; this reduces to selecting positions to keep so that for every same-length dictionary word at least one kept position differs, solvable by filtering same-length words and searching bitmask patterns (with bit operations/pruning) for the minimum-length distinguishing mask.