LeetCode-Best Time to Buy and Sell Stock IV -解题报告

原题链接https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/

Say you have an array for which the i^th element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete at most k transactions.

Note:
You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

和第三题类似，使用动态规划，我们发现对于一个大小为n的数组来说，最多交易n/2次，因此对于k>= n/2的情况，就退化成第2版的情况，所以只需要将大于0的加起来就行了

class Solution {
public:
    int maxProfit(int k, vector& prices) {
		if (prices.size() < 2)return 0;
		vectorcur(prices.size(), 0);
		vectorpre(prices.size(), 0);
		vectornums(prices.size());
		int Max = 0;
		for (int i = 1; i < prices.size(); ++i)
			nums[i] = prices[i] - prices[i - 1];
		if (k >= prices.size() / 2)
		{
			for (int i = 1; i < prices.size(); ++i)
			if (nums[i] > 0)Max += nums[i];
			return Max;
		}
		for (int j = 1; j <= k; ++j)
		{
			Max = 0;
			for (int i = j; i < prices.size(); ++i)
			{
				cur[i] = max(cur[i - 1], pre[i - 1]) + nums[i];
				pre[i - 1] = Max;
				if (cur[i] > pre[i - 1])
					Max = cur[i];
			}
		}

		return Max;
	}
};