struct Solution {}
use std::cmp::max;
impl Solution {
    pub fn max_profit(prices: Vec<i32>) -> i32 {
        if prices.len() <= 0 {
            return 0;
        }
        let mut min = prices[0];
        let mut profit = 0;
        for i in 1..prices.len() {
            let p = prices[i];
            profit = max(profit, p - min);
            if p < min {
                min = p;
            }
        }
        profit
    }
}