LeetCode in Racket
121. Best Time to Buy and Sell Stock
Easy
You are given an array prices where prices[i] is the price of a given stock on the ith day.
You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.
Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.
Example 1:
Input: prices = [7,1,5,3,6,4]
Output: 5
Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
Example 2:
Input: prices = [7,6,4,3,1]
Output: 0
Explanation: In this case, no transactions are done and the max profit = 0.
Constraints:
1 <= prices.length <= 1050 <= prices[i] <= 104
Solution
(define/contract (max-profit prices)
(-> (listof exact-integer?) exact-integer?)
(if (empty? prices)
0
(let-values ([(final-profit _)
(for/fold ([max-profit 0]
[min-price (first prices)])
([price (in-list (rest prices))])
(if (> price min-price)
(values (max max-profit (- price min-price))
min-price)
(values max-profit price)))])
final-profit)))