# missjing/leetcode

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 problem: 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). ----------------------------------------------------------------------- solution: //限制只有两次交易，不过交易不重叠 //设i从0~n-1，针对每个i，对子序列[0..i],[i..n-1]上分别求最大利润 int maxProfit(vector &prices) { if(prices.size() == 0) return 0; vector f1(prices.size()); vector f2(prices.size()); int minV = prices[0]; f1[0] = 0; for(int i = 1; i < prices.size(); ++i) { minV = min(minV, prices[i]); f1[i] = max(f1[i - 1], prices[i] - minV); } int maxV = prices[prices.size() - 1]; f2[f2.size() - 1] = 0; for(int i = prices.size() - 2; i >= 0; --i) { maxV = max(maxV, prices[i]); f2[i] = max(f2[i + 1], maxV - prices[i]); } int sum = 0; for(int i = 0; i < prices.size(); ++i) sum = max(sum, f1[i] + f2[i]); return sum; }