188. Best Time to Buy and Sell Stock IV

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LeetCode

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Problem

You are given an integer array prices where prices[i] is the price of a given stock on the ith day, and an integer k.

Find the maximum profit you can achieve. You may complete at most k transactions.

Note: You may not engage in multiple transactions simultaneously (i.e., you must sell the stock before you buy again).

Example 1:

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

Example 2:

Input: k = 2, prices = [3,2,6,5,0,3]
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.

Code

class Solution {
    public int maxProfit(int k, int[] prices) {
        int len = prices.length;
        
        if(k >= len / 2) return helper(prices);
        
        int[][] dp = new int[k + 1][prices.length];
        
        for(int i = 1; i <= k; i++){
            for(int j = 1; j < prices.length; j++){
                int max = 0;
                for(int m = 0; m < j; m++){
                    max = Math.max(max, dp[i - 1][m] - prices[m] + prices[j]);
                }
                
                dp[i][j] = Math.max(dp[i][j - 1], max);
            }
            
            
        }
        return dp[k][prices.length - 1];
    }
    
    private int helper(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;
    }
}