188. 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).

Example 1:

Input: [2,4,1], k = 2
Output: 2
Explanation: Buy on day 1 (price = 2) and sell on day 2 (price = 4), profit = 4-2 = 2.

Example 2:

Input: [3,2,6,5,0,3], k = 2
Output: 7
Explanation: Buy on day 2 (price = 2) and sell on day 3 (price = 6), profit = 6-2 = 4.
             Then buy on day 5 (price = 0) and sell on day 6 (price = 3), profit = 3-0 = 3.

class Solution {
    public int maxProfit(int k, int[] prices) {
        int l = prices.length;
        if(l==0) return 0;
        if(k >= l) return btbs2(prices);
        int[][] global = new int[l][k+1];
        int[][] local = new int[l][k+1];
        
        for(int i = 1; i < l; i++){
            int diff = prices[i] - prices[i-1];
            
            for(int j = 1; j <= k; j++){
                local[i][j] = Math.max(global[i-1][j-1]+Math.max(0, diff), local[i-1][j] + diff); // Math.max似乎是多余的
                global[i][j] = Math.max(global[i-1][j], local[i][j]);
            }
        }
        return global[l-1][k];
    }
    public int btbs2(int[] prices){
        int res = 0;
        
        for(int i = 1; i < prices.length; i++){
            if(prices[i] > prices[i-1]) res += prices[i] - prices[i-1];
        }
        return res;
    }
}

这题是真他妈难。

不错的讲解：http://www.360doc.com/content/16/1004/16/10408243_595735141.shtml

https://blog.csdn.net/linhuanmars/article/details/23236995

https://www.cnblogs.com/grandyang/p/4295761.html