121. Best Time to Buy and Sell Stock

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 <= 105
• 0 <= prices[i] <= 104

121. Best Time to Buy and Sell Stock
struct Solution;

impl Solution {
fn max_profit(prices: Vec<i32>) -> i32 {
let mut cost = std::i32::MAX;
let mut profit = 0;
for price in prices {
profit = profit.max(price - cost);
cost = cost.min(price);
}
profit
}
}

#[test]
fn test() {
let prices = vec![7, 1, 5, 3, 6, 4];
let res = 5;
assert_eq!(Solution::max_profit(prices), res);
let prices = vec![7, 6, 4, 3, 1];
let res = 0;
assert_eq!(Solution::max_profit(prices), res);
}