LeetCode 121. Best Time to Buy and Sell Stock

/**
 * @param {number[]} prices
 * @return {number}
 */
var maxProfit = function(prices) {
    let l = 0;
    let r = 1;
    let maxProfit = 0;
    
    while(r < prices.length) {
        if (prices[l] < prices[r]) {
            // Profitable transaction
            const profit = prices[r] - prices[l];
            maxProfit = Math.max(maxProfit, profit);
        } else {
            // Not Profitable transaction
            l = r;
        }
        r++;
    }
    
    return maxProfit;
};