Day 37

Best Time to Buy and Sell Stock

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class Solution {
    public int maxProfit(int[] prices) {
        int[][] dp = new int[prices.length][2];
        dp[0][0] = -prices[0];
        dp[0][1] = 0;

        for (int i = 1; i < prices.length; i++) {
            // ith day maximum profit with stock， not buy or buy
            dp[i][0] = Math.max(dp[i - 1][0], -prices[i]);
            // ith day maximum profit without stock， not sell or sell
            dp[i][1] = Math.max(dp[i - 1][1], dp[i - 1][0] + prices[i]);
        }

        // last day sell stock, maximun profit
        return dp[prices.length - 1][1];
    }
}
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func maxProfit(prices []int) int {
	dp := make([][]int, len(prices))
	for i := 0; i < len(prices); i++ {
		dp[i] = make([]int, 2)
	}

	dp[0][0] = -prices[0]
	dp[0][1] = 0

	for i := 1; i < len(prices); i++ {
		dp[i][0] = max(dp[i-1][0], -prices[i])
		dp[i][1] = max(dp[i-1][1], dp[i-1][0]+prices[i])
	}
	return dp[len(prices)-1][1]
}

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

Best Time to Buy and Sell Stock II

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class Solution {
    public int maxProfit(int[] prices) {
        // int res = 0;
        // for (int i = 1; i < prices.length; i++) {
        //     res += Math.max(prices[i] - prices[i - 1], 0);
        // }
        // return res;

        int[][] dp = new int[prices.length][2];
        dp[0][0] = -prices[0];
        dp[0][1] = 0;

        for (int i = 1; i < prices.length; i++) {
            dp[i][0] = Math.max(dp[i - 1][0], dp[i - 1][1] - prices[i]);
            dp[i][1] = Math.max(dp[i - 1][1], dp[i - 1][0] + prices[i]);
        }

        return dp[prices.length - 1][1];
    }
}
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func maxProfit(prices []int) int {
	dp := make([][]int, len(prices))
	for i := 0; i < len(prices); i++ {
		dp[i] = make([]int, 2)
	}

	dp[0][0] = -prices[0]
	dp[0][1] = 0

	for i := 1; i < len(prices); i++ {
		dp[i][0] = max(dp[i-1][0], dp[i-1][1]-prices[i])
		dp[i][1] = max(dp[i-1][1], dp[i-1][0]+prices[i])
	}
	return dp[len(prices)-1][1]
}

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

Best Time to Buy and Sell Stock III

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class Solution {
    public int maxProfit(int[] prices) {
        int[] dp = new int[5];
        dp[1] = -prices[0];
        dp[3] = -prices[0];

        for (int i = 1; i < prices.length; i++) {
            dp[1] = Math.max(dp[1], dp[0] - prices[i]);
            dp[2] = Math.max(dp[2], dp[1] + prices[i]);
            dp[3] = Math.max(dp[3], dp[2] - prices[i]);
            dp[4] = Math.max(dp[4], dp[3] + prices[i]);
        }
        return dp[4];
    }
}
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func maxProfit(prices []int) int {
	if len(prices) == 0 {
		return 0
	}
	dp := make([]int, 5)
	dp[1] = -prices[0]
	dp[3] = -prices[0]
	for i := 1; i < len(prices); i++ {
		dp[1] = max(dp[1], dp[0]-prices[i])
		dp[2] = max(dp[2], dp[1]+prices[i])
		dp[3] = max(dp[3], dp[2]-prices[i])
		dp[4] = max(dp[4], dp[3]+prices[i])
	}
	return dp[4]
}

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