Description (leetcode)

You are given an array prices where prices[i] is the price of a given stock on the i^th day.

Find the maximum profit you can achieve. You may complete at most two transactions.

Note: You may not engage in multiple transactions simultaneously (i.e., you must sell the stock before you buy again).

Example 1:

Input: prices = [3,3,5,0,0,3,1,4]

Output: 6

Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3), profit = 3-0 = 3.

Then buy on day 7 (price = 1) and sell on day 8 (price = 4), profit = 4-1 = 3.

Example 2:

Input: prices = [1,2,3,4,5]

Output: 4

Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.

Note that you cannot buy on day 1, buy on day 2 and sell them later, as you are engaging multiple transactions at the same time. You must sell before buying again.

Example 3:

Input: prices = [7,6,4,3,1]

Output: 0

Explanation: In this case, no transaction is done, i.e. max profit = 0.

Constraints:

  • 1 <= prices.length <= 10^5
  • 0 <= prices[i] <= 10^5

submission

impl Solution {
    pub fn max_profit(prices: Vec<i32>) -> i32 {
        // stateful dp
        prices.into_iter()
            .fold([(i32::MIN, 0); 3], |mut dp, price| {
                dp[1].0 = dp[1].0.max(dp[0].1 - price);
                dp[1].1 = dp[1].1.max(dp[1].0 + price);
                dp[2].0 = dp[2].0.max(dp[1].1 - price);
                dp[2].1 = dp[2].1.max(dp[2].0 + price);
                dp
            })[2].1
    }
}