Leetcode 2222. Number of Ways to Select Buildings

Count the number of index triples i<j<k in a binary string that form an alternating pattern "010" or "101" (so no two consecutive selected buildings have the same type). This reduces to summing, for each middle index, the product of opposite-bit counts on its left and right (can be done with prefix/suffix counts in O(n)).

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Leetcode 2222. Number of Ways to Select Buildings

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