188. Best Time to Buy and Sell Stock IV

Say you have an array for which the ith 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.

一刷
dynamic programming

public class Solution {
    public int maxProfit(int k, int[] prices) {
        int len = prices.length;
        if(len == 0 || k<=0) return 0;
        if(k >= len/2) return greedy(prices);
        int[] hold = new int[k];
        int[] sold = new int[k];
        Arrays.fill(hold, -prices[0]);
        int max = 0;
        for(int i=1; i0; j--){
                sold[j] = Math.max(sold[j], prices[i] + hold[j]);
                hold[j] = Math.max(hold[j], sold[j-1] - prices[i]);
            }
            sold[0] = Math.max(sold[0], prices[i] + hold[0]);
            hold[0] = Math.max(hold[0], -prices[i]);
        }
        return sold[k-1];
    }
    
    private int greedy(int[] prices){
        int res = 0;
        for(int i=1; iprices[i-1]) res += prices[i] - prices[i-1];
        }
        return res;
    }
}