leetcode数组专项习题：股票买卖问题-III

4、买卖股票的最佳时间-III
best-time-to-buy-and-sell-stock-iii: 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 two transactions.
Note: You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
题目要求：假设有一个数组，其中第i个元素是第i天给定股票的价格。设计算法以找到最大利润。 最多可以完成两笔交易。
注意：不能同时进行多笔交易（必须在再次购买之前卖出股票）。
分析：

class Solution {
    public int maxProfit(int[] prices) {  
        int buy1=Integer.MIN_VALUE;
        int buy2=Integer.MIN_VALUE;
        int sell1=0;
        int sell2=0;

        for(int i=0;i<prices.length;i++){
            buy1=Math.max(buy1,-prices[i]);
            sell1=Math.max(sell1,buy1+prices[i]);
            buy2=Math.max(buy2,sell1-prices[i]);
            sell2=Math.max(sell2,buy2+prices[i]);
        }
        return sell2;
    }  
}