原题链接：Leetcode 983. 最低票价

class Solution {
public:
    int mincostTickets(vector<int>& days, vector<int>& costs) {
        int n = days.size();
        int last = days[n - 1];
        int dp[last + 1];
        map<int, int> mp;
        for (auto x : days)
            mp[x] = 1;
        dp[0] = 0;
        int v1[3] = {1, 7, 30};
        for (int i = 1; i <= last; i++) {
            if (mp[i]) {
                dp[i] = INT_MAX;
                for (int k = 0; k < 3; k++) {
                    dp[i] = min(dp[i], dp[max(i - v1[k], 0)] + costs[k]);
                }
            } else {
                dp[i] = dp[i - 1];
            }
        }
        return dp[last];
    }
};