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2909. Minimum Sum of Mountain Triplets II

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class Solution:
    def minimumSum(self, nums: List[int]) -> int:

        N = len(nums)
        INF = 10 ** 20

        def gen(lst):

            res = [INF]

            for i in range(len(lst)):
                res.append(min(lst[i], res[-1]))

            return res

        prefix = gen(nums)
        suffix = gen(nums[::-1])[::-1]

        res = INF

        for i in range(1, N-1):
            if prefix[i] < nums[i] and nums[i] > suffix[i+1]:
                res = min(res, prefix[i] + nums[i] + suffix[i+1])

        return res if res != INF else -1