122 best time to buy and sell stock ii

122. 买卖股票的最佳时机 II

go：

func maxProfit(prices []int) int {
    if len(prices) == 0 {
        return 0
    }
    cash, hold := 0, -prices[0]

    for i := 1; i < len(prices); i++ {
        preCash, preHold := cash, hold
        cash = max(preCash, preHold + prices[i])
        hold = max(preHold, preCash - prices[i])
    }

    return cash
}

func max(a, b int) int {
    if a < b {
        return b
    }
    return a
}