Week 2019-06-30

买卖股票的最佳时机 I

func maxProfit(prices []int) int {
    maxProfit := 0
    minPrice := math.MaxInt64
    for _, v := range prices {
        minPrice = mymin(minPrice, v)
        maxProfit = mymax(maxProfit, v-minPrice)
    }
    return maxProfit
}
func mymin(x, y int) int {
    if x > y {
        return y
    }
    return x
}
func mymax(x, y int) int {
    if x > y {
        return x
    }
    return y
}

买卖股票的最佳时机 II

func maxProfit(prices []int) int {
    cur, max := 0, 0
    for i := 1; i < len(prices); i++ {
        cur = mymax(cur, cur+prices[i]-prices[i-1])
        max = mymax(cur, max)
    }
    return max
}
func mymax(x, y int) int {
    if x > y {
        return x
    }
    return y
}

买卖股票的最佳时机 III

/**
只能进行两次交易，因此一共有四个状态，互相之间转移
*/

func maxProfit(prices []int) int {
    b1, b2 := math.MinInt32, math.MinInt32
    s1, s2 := 0, 0
    for i := 0; i < len(prices); i++ {
        b1 = max(b1, -prices[i])
        s1 = max(s1, b1+prices[i])
        b2 = max(b2, s1-prices[i])
        s2 = max(s2, b2+prices[i])
    }
    return s2
}

func max(x, y int) int {
    if x > y {
        return x
    }
    return y
}