LeetCode 188. Best Time to Buy and Sell Stock IV (stock 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 k transactions.

Note:

You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

分析

依然是stock problem模型，但这次必须压缩空间，否则超限，并且在 k>prices.size() 时，转化为k=+无穷的情况，否则超限。

const int inf=-999999;
class Solution {
public:
    int maxProfit(int k, vector<int>& prices) {
     if(prices.size()<=1) return 0;
     if (k >= prices.size()) {
        int T_ik0 = 0, T_ik1 =inf;
        for (auto price : prices) {
            T_ik1 = max(T_ik1, T_ik0 - price);
            T_ik0 = max(T_ik0, T_ik1 + price);
        }
        return T_ik0;
     }
        int sell[k+1]={0},buy[k+1];
        fill(buy,buy+k+1,inf);
        for(int i=0;i<prices.size();i++)
            for(int j=1;j<=k;j++){
                sell[j]=max(sell[j],buy[j]+prices[i]);
                buy[j]=max(buy[j],sell[j-1]-prices[i]);
            }
        return sell[k];
    }
};