123. Best Time to Buy and Sell Stock III

leetcode 123.123. Best Time to Buy and Sell Stock III 困难

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 (i.e., you must sell the stock before you buy again).

Example 1:

Input: [3,3,5,0,0,3,1,4]
Output: 6
Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3), profit = 3-0 = 3.

         Then buy on day 7 (price = 1) and sell on day 8 (price = 4), profit = 4-1 = 3.

Example 2:

Input: [1,2,3,4,5]
Output: 4
Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.

         Note that you cannot buy on day 1, buy on day 2 and sell them later, as you are
         engaging multiple transactions at the same time. You must sell before buying again.

Example 3:

Input: [7,6,4,3,1]
Output: 0
Explanation: In this case, no transaction is done, i.e. max profit = 0.

class Solution {
public:
    int maxProfit(vector<int>& prices) {
        int len = prices.size();
        if(len == 0 ){
            return 0;
        }
        int firstbuy = 1<<30;
        int firstsell = - (1<<30);
        int secondbuy = - (1<<30);
        int secondsell = - (1<<30);
        for(int i = 0 ;i < len; ++i){
            firstbuy = min(firstbuy,prices[i]);
            firstsell = max(firstsell,prices[i]-firstbuy);
            secondbuy = max(secondbuy,firstsell - prices[i]);
            secondsell = max(secondsell,prices[i] + secondbuy);
        }
        return secondsell;
    }
};
Last modification:December 29th, 2019 at 03:25 am
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