5776: Stock Trading
内存限制：256 MB
时间限制：2 S
题面：传统
评测方式：文本比较
上传者：
提交：1
通过：1
题目描述
F3. Stock Trading
time limit per test
3 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
This problem consists of three subproblems: for solving subproblem F1 you will receive 8 points, for solving subproblem F2 you will receive 15 points, and for solving subproblem F3 you will receive 10 points.
Manao has developed a model to predict the stock price of a company over the next n days and wants to design a profit-maximizing trading algorithm to make use of these predictions. Unfortunately, Manao's trading account has the following restrictions:
Even though these restrictions limit the amount of profit Manao can make compared to what would be achievable with an unlimited number of trades or the ability to hold more than one share at a time, Manao still has the potential to make a lot of money because Manao's model perfectly predicts the daily price of the stock. For example, using this model, Manao could wait until the price is low, then buy one share and hold until the price reaches a high value, then sell for a profit, and repeat this process up to k times until n days have passed.
Nevertheless, Manao is not satisfied by having a merely good trading algorithm, and wants to develop an optimal strategy for trading subject to these constraints. Help Manao achieve this goal by writing a program that will determine when to buy and sell stock to achieve the greatest possible profit during the n-day trading period subject to the above constraints.
Manao has developed a model to predict the stock price of a company over the next n days and wants to design a profit-maximizing trading algorithm to make use of these predictions. Unfortunately, Manao's trading account has the following restrictions:
- It only allows owning either zero or one shares of stock at a time;
- It only allows buying or selling a share of this stock once per day;
- It allows a maximum of k buy orders over the next n days;
Even though these restrictions limit the amount of profit Manao can make compared to what would be achievable with an unlimited number of trades or the ability to hold more than one share at a time, Manao still has the potential to make a lot of money because Manao's model perfectly predicts the daily price of the stock. For example, using this model, Manao could wait until the price is low, then buy one share and hold until the price reaches a high value, then sell for a profit, and repeat this process up to k times until n days have passed.
Nevertheless, Manao is not satisfied by having a merely good trading algorithm, and wants to develop an optimal strategy for trading subject to these constraints. Help Manao achieve this goal by writing a program that will determine when to buy and sell stock to achieve the greatest possible profit during the n-day trading period subject to the above constraints.
Input
The first line contains two integers n and k, separated by a single space, with 
. The i-th of the following n lines contains a single integer pi (0≤pi≤1012), where pi represents the price at which someone can either buy or sell one share of stock on day i.
The problem consists of three subproblems. The subproblems have different constraints on the input. You will get some score for the correct submission of the subproblem. The desc
- In subproblem F1 (8 points), n will be between 1 and 3000, inclusive.
- In subproblem F2 (15 points), n will be between 1 and 100000, inclusive.
- In subproblem F3 (10 points), n will be between 1 and 4000000, inclusive.
Output
For this problem, the program will only report the amount of the optimal profit, rather than a list of trades that can achieve this profit.
Therefore, the program should print one line containing a single integer, the maximum profit Manao can achieve over the next n days with the constraints of starting with no shares on the first day of trading, always owning either zero or one shares of stock, and buying at most k shares over the course of the n-day trading period.
Examples
Input
10 2 2 7 3 9 8 7 9 7 1 9
Output
15
Input
10 5 2 7 3 9 8 7 9 7 1 9
Output
21
Note
In the first example, the best trade overall is to buy at a price of 1 on day 9 and sell at a price of 9 on day 10 and the second best trade overall is to buy at a price of 2 on day 1 and sell at a price of 9 on day 4. Since these two trades do not overlap, both can be made and the profit is the sum of the profits of the two trades. Thus the trade strategy looks like this:
2 | 7 | 3 | 9 | 8 | 7 | 9 | 7 | 1 | 9 buy | | | sell | | | | | buy | sellThe total profit is then (9-2)+(9-1)=15.
In the second example, even though Manao is allowed up to 5 trades there are only 4 profitable trades available. Making a fifth trade would cost Manao money so he only makes the following 4:
2 | 7 | 3 | 9 | 8 | 7 | 9 | 7 | 1 | 9 buy | sell | buy | sell | | buy | sell | | buy | sellThe total profit is then (7-2)+(9-3)+(9-7)+(9-1)=21.
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