func maxProfit(prices []int) int {
    l,r:=0,1 // buy, sell
    maxP:=0

    for r < len(prices) {
        if prices[l] < prices[r] {
            profit := prices[r] - prices[l]
            maxP = max(maxP, profit)
        }else {
            l = r
        }
        r +=1
    }
    return maxP
}

func max(l,r int )int {
    if l > r {
        return l
    }
    return r
}