121-Best-Time-to-Buy-and-Sell-Stock.js

/**
 * @param {number[]} prices
 * @return {number}
 */
var maxProfit = function(prices) {
    let buy = prices[0];
    let profit = 0; 
    for (let i = 0; i < prices.length; i++) {
        if (prices[i] < buy) {
            buy = prices[i];
        } else {
            profit = Math.max(prices[i] - buy, profit);
        }
    }
    return profit;
};