LeetCode/problems/rs/best-time-to-buy-and-sell-stock-iv.rs

#[derive(Debug)]
struct State {
    price: i32,
    profit: i32,
}

impl State {
    fn new() -> State {
        State {
            price: i32::MAX,
            profit: 0,
        }
    }

    fn update(&self, previous: &State, price: i32) -> State {
        let new_price = std::cmp::min(self.price, price - previous.profit);

        State {
            price: new_price,
            profit: std::cmp::max(self.profit, price - new_price),
        }
    }
}

impl Solution {
    pub fn max_profit(k: i32, prices: Vec<i32>) -> i32 {
        let mut states: Vec<State> = (0..=k).map(|_| State::new()).collect();

        prices.iter().for_each(|p| {
            let mut new_states = Vec::from([State::new()]);

            new_states.extend(
                states
                    .iter()
                    .zip(states.iter().skip(1))
                    .map(|(prev_state, state)| state.update(prev_state, *p)),
            );

            states = new_states;
        });

        states.last().expect("No state is present").profit
    }
}
struct Solution {}

fn main() {
    println!("Hello World!");
}

#[cfg(test)]
mod tests_max_profit {
    use super::*;

    #[test]
    fn test_small_example() {
        assert_eq!(Solution::max_profit(2, vec![2, 4, 1]), 2);
    }

    #[test]
    fn test_bigger_example() {
        assert_eq!(Solution::max_profit(2, vec![3, 2, 6, 5, 0, 3]), 7);
    }

    #[test]
    fn test_small_no_transaction() {
        assert_eq!(Solution::max_profit(0, vec![2, 4, 1]), 0);
    }

    #[test]
    fn test_small_one_transaction() {
        assert_eq!(Solution::max_profit(1, vec![2, 4, 1]), 2);
    }

    #[test]
    fn test_bigger_one_transaction() {
        assert_eq!(Solution::max_profit(1, vec![3, 2, 6, 5, 0, 3]), 4);
    }

    #[test]
    fn test_big_all_transactions() {
        assert_eq!(
            Solution::max_profit(10, vec![3, 2, 6, 5, 0, 3, 1, 13, 5, 2, 1, 9, 4, 5, 69, 42]),
            92
        );
    }

    #[test]
    fn test_buy_expensive() {
        assert_eq!(Solution::max_profit(2, vec![2, 3, 14, 15]), 13);
    }

    #[test]
    fn test_accumulates_profit() {
        assert_eq!(Solution::max_profit(5, vec![1, 2, 1, 2, 1, 2, 1, 2, 5]), 7);
    }

    #[test]
    fn test_no_profit_made() {
        assert_eq!(Solution::max_profit(2, vec![5, 4]), 0);
    }
}