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

Rust Solution

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);
}

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