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/**

* 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

* two transactions.

*

* Note:

* You may not engage in multiple transactions at the same time (ie, you must

* sell the stock before you buy again).

*

*/

public class BestTimeToBuyAndSellStockIII123 {

public int maxProfit(int[] prices) {

if (prices == null || prices.length <= 1) return 0;

int buy = Integer.MIN_VALUE;

int preBuy = Integer.MIN_VALUE;

int sell = 0;

int preSell = 0;

for (int p: prices) {

sell = Math.max(sell, buy + p);

buy = Math.max(buy, preSell - p);

preSell = Math.max(preSell, preBuy + p);

preBuy = Math.max(preBuy, - p);

}

return sell;

}

public int maxProfit2(int[] prices) {

return maxProfit(2, prices);

}

public int maxProfit(int k, int[] prices) {

if (prices == null || prices.length <= 1 || k <= 0) return 0;

if (k >= prices.length >>> 1) {

int profit = 0;

for(int i=1; i<prices.length; i++){

if(prices[i] > prices[i-1]){

profit += prices[i] - prices[i-1];

}

}

return profit;

}

int[] buy = new int[k+1];

int[] sell = new int[k+1];

for (int j=0; j<=k; j++) {

buy[j] = Integer.MIN_VALUE;

}

for (int price : prices) {

for (int j=1; j<=k; j++) {

buy[j] = Math.max(buy[j], sell[j-1] - price);

sell[j] = Math.max(sell[j], buy[j] + price);

}

}

return sell[k];

}

}