動態規劃：

1.class Solution {
    public int maxProfit(int[] prices) {
        int[] profit = new int[prices.length];
        if(prices.length==0)
			return 0;
	for (int i = 0; i < prices.length; i++)
		for (int j = 0; j < i; j++)
			profit[i] = Math.max(profit[j] + prices[i] - prices[j], profit[i - 1]);
        return profit[prices.length-1];
    }
}
2.class Solution {
    public int maxProfit(int[] prices) {
        int[] profit = new int[prices.length];
        if(prices.length==0)
			return 0;
	for (int i = 1; i < prices.length; i++)
		profit[i] = Math.max(profit[i - 1] + prices[i] - prices[i - 1], profit[i - 1]);
        return profit[prices.length-1];
    }
}
 

這題有點怪，我的理解好像有點出錯

public class MaxProfit122 {
	public static void main(String[] args) {
		int[] prices = { 7, 1, 5, 3, 6, 7 };

		if (prices.length < 2)
			System.out.println(0);
		int sum = 0;
		for (int i = 0; i < prices.length - 1; i++)
			if (prices[i + 1] - prices[i] > 0)
				sum += prices[i + 1] - prices[i];
		System.out.println(sum);

	}
}