leetcode-983 最低票价 Python

https://leetcode-cn.com/problems/minimum-cost-for-tickets/solution/zui-di-piao-jie-by-leetcode-solution/

方法一：

class Solution {
    int[] costs;
    Integer[] memo;
    Set<Integer> dayset;
    
    public int mincostTickets(int[] days, int[] costs) {
        this.costs = costs;
        memo = new Integer[366];
        dayset = new HashSet();
        for (int d: days) {
            dayset.add(d);
        }
        return dp(1) ;   
    }
    public int dp(int i) {
        if (i > 365) {
            return 0;
        }
        if (memo[i] != null) {
            return memo[i];
        }
        if (dayset.contains(i)) {
            memo[i] = Math.min(Math.min(dp(i + 1) + costs[0], dp(i + 7) + costs[1]), dp(i + 30) + costs[2]);
        } else {
            memo[i] = dp(i + 1);
        }
        return memo[i];
    }
}

方法二：

class Solution {
    int[] costs,days;
    Integer[] memo;
    int[] durations = new int[] {1, 7, 30};
    
    public int mincostTickets(int[] days, int[] costs) {
        this.days = days;
        this.costs = costs;
        memo = new Integer[days.length];
        return dp(0);
    }

    public int dp(int i) {
        if (i >= days.length) {
            return 0;
        }
        if (memo[i] != null) {
            return memo[i];
        }
        memo[i] = Integer.MAX_VALUE;
        int j = i;
        for (int k = 0; k < 3; ++k) {
            while (j < days.length && days[j] < days[i] + durations[k]) {
                j++;
            }
            memo[i] = Math.min(memo[i], dp(j) + costs[k]);
        }
        return memo[i];
    }
}