983. Minimum Cost For Tickets

In a country popular for train travel, you have planned some train travelling one year in advance.  The days of the year that you will travel is given as an array `days`.  Each day is an integer from `1` to `365`.

Train tickets are sold in 3 different ways:

• a 1-day pass is sold for `costs[0]` dollars;
• a 7-day pass is sold for `costs[1]` dollars;
• a 30-day pass is sold for `costs[2]` dollars.

The passes allow that many days of consecutive travel.  For example, if we get a 7-day pass on day 2, then we can travel for 7 days: day 2, 3, 4, 5, 6, 7, and 8.

Return the minimum number of dollars you need to travel every day in the given list of `days`.

Example 1:

```Input: days = [1,4,6,7,8,20], costs = [2,7,15]
Output: 11
Explanation:
For example, here is one way to buy passes that lets you travel your travel plan:
On day 1, you bought a 1-day pass for costs[0] = \$2, which covered day 1.
On day 3, you bought a 7-day pass for costs[1] = \$7, which covered days 3, 4, ..., 9.
On day 20, you bought a 1-day pass for costs[0] = \$2, which covered day 20.
In total you spent \$11 and covered all the days of your travel.
```

Example 2:

```Input: days = [1,2,3,4,5,6,7,8,9,10,30,31], costs = [2,7,15]
Output: 17
Explanation:
For example, here is one way to buy passes that lets you travel your travel plan:
On day 1, you bought a 30-day pass for costs[2] = \$15 which covered days 1, 2, ..., 30.
On day 31, you bought a 1-day pass for costs[0] = \$2 which covered day 31.
In total you spent \$17 and covered all the days of your travel.
```

Note:

1. `1 <= days.length <= 365`
2. `1 <= days[i] <= 365`
3. `days` is in strictly increasing order.
4. `costs.length == 3`
5. `1 <= costs[i] <= 1000`

983. Minimum Cost For Tickets
``````struct Solution;

impl Solution {
fn mincost_tickets(days: Vec<i32>, costs: Vec<i32>) -> i32 {
let n = days.len();
let mut dp: Vec<i32> = vec![];
let pass = vec![1, 7, 30];
for i in 0..n {
let mut mins = costs.clone();
for k in 0..3 {
for j in (0..i).rev() {
if days[i] - days[j] >= pass[k] {
mins[k] += dp[j];
break;
}
}
}
dp.push(*mins.iter().min().unwrap());
}
dp[n - 1]
}
}

#[test]
fn test() {
let days = vec![1, 4, 6, 7, 8, 20];
let costs = vec![2, 7, 15];
let res = 11;
assert_eq!(Solution::mincost_tickets(days, costs), res);
let days = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 30, 31];
let costs = vec![2, 7, 15];
let res = 17;
assert_eq!(Solution::mincost_tickets(days, costs), res);
}
``````