983. Minimum Cost For Tickets

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目標 dp[i] 是當在旅程從第 i 天開始，完成所有旅程所需要的最少成本。

class Solution:
    def mincostTickets(self, days: List[int], costs: List[int]) -> int:
        dayset = set(days)
        m = max(days)
        costTable = {
            1: costs[0],
            7: costs[1],
            30: costs[2]
        }
        @cache
        def dp(day):
            if day > m:
                return 0
            if day in dayset:
                return min(dp(day + key) + val for key, val in costTable.items())
            return dp(day + 1)
        return dp(1)