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Leetcode188-bestTimeToBuyAndSellStockIV

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Solution Report of LeetCode Acceptted

Description

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

Example 1:

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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:
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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.

Solution

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