best_time_to_buy_and_sell_stock.rs

/// 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`.
struct Solution;

impl Solution {
    pub fn max_profit(prices: Vec<i32>) -> i32 {
        let n = prices.len();
        let mut profit = 0;
        let mut buy = prices[0];

        for i in 1..n {
            profit = profit.max(prices[i] - buy);
            buy = buy.min(prices[i]);
        }

        profit
    }
}

#[cfg(test)]
mod tests {
    use super::Solution;

    #[test]
    fn example_1() {
        let prices = vec![7, 1, 5, 3, 6, 4];
        let result = Solution::max_profit(prices);
        assert_eq!(result, 5);
    }

    #[test]
    fn example_2() {
        let prices = vec![7, 6, 4, 3, 1];
        let result = Solution::max_profit(prices);
        assert_eq!(result, 0);
    }
}