7454번 - Keep the Customer Satisfied 다국어

Simon and Garfunkel Corporation (SG Corp.) is a large steel-making company with thousand of customers. Keeping the customer satisfied is one of the major objective of Paul and Art, the managers.

Customers issue orders that are characterized by two integer values q, the amount of steel required (in tons) and d, the due date (a calender date converted in seconds). The due date has to be met if SG Corp. accepts the order. Stated another way, when an order is accepted, the corresponding amount of steel has to be produced before its due date. Of course, the factory can process no more than one order at a time.

Although the manufacturing process is rather complex, it can be seen as a single production line with a constant throughput. In the following, we assume that producing q tons of steel takes exactly q seconds (i.e., throughput is 1). The factory runs on a monthly production plan. Before the beginning of the month, all customers’ orders are collected and Paul and Art determine which of them are going to be accepted and which ones are to be rejected in the next production period. A production schedule is then designed. To keep customers satisfied, Paul and Art want to minimize the total number of orders that are rejected. In the following, we assume that the beginning of the next production plan (i.e., the first day of the next month) corresponds to date 0.

Hogdson and Moore have been appointed as Chief Scientific Officers and you are requested to help them to compute an optimal solution and to build a schedule of all accepted orders (starting time and completion time).

Consider the following data set made of 6 orders J₁, ..., J₆. For a given order, J_j, q_j denotes the amount of steel required and d_j is the associated due date.

You can check by hand that all orders cannot be accepted and it’s very unlikely you could find a solution with less than two rejected orders. Here is an optimal solution: Reject J₁ and J₄, accept all other orders and process them as follows.

Note that the production line is never idle.

Each test case is described by one input file that contains all the relevant data: The first line contains the number n of orders (n can be as large as 800000 for some test cases). It is followed by n lines. Each of which describes an order made of two integer values: the amount of steel (in tons) required for the order (lower than 1000) and its due date (in seconds; lower than 2 × 10⁶).

You are required to compute an optimal solution and your program has to write the number of orders that are accepted.

• Hogdson and Moore claim that it is optimal to sequence accepted orders in non-decreasing order of due dates.
• They also claim that there is an optimal solution such that for any two orders J_u and J_v with q_u > q_v and d_u < d_v, if Ju is accepted then Jv is also accepted.
• Finally, Hogdson and Moore advise you to “Keep the Customer Satisfied”