Problem:
Score : 400 points

Problem Statement

There are N one-off jobs available. If you take the i-th job and complete it, you will earn the reward of B_i after A_i days from the day you do it.

You can take and complete at most one of these jobs in a day.

However, you cannot retake a job that you have already done.

Find the maximum total reward that you can earn no later than M days from today.

You can already start working today.

Constraints

All values in input are integers.

1 \leq N \leq 10^5

1 \leq M \leq 10^5

1 \leq A_i \leq 10^5

1 \leq B_i \leq 10^4

Input

Input is given from Standard Input in the following format:

N M
A_1 B_1
A_2 B_2
\vdots
A_N B_N

Output

Print the maximum total reward that you can earn no later than M days from today.

Sample Input 1

3 4
4 3
4 1
2 2

Sample Output 1

5

You can earn the total reward of 5 by taking the jobs as follows:

Take and complete the first job today. You will earn the reward of 3 after four days from today.

Take and complete the third job tomorrow. You will earn the reward of 2 after two days from tomorrow, that is, after three days from today.

Sample Input 2

5 3
1 2
1 3
1 4
2 1
2 3

Sample Output 2

10

Sample Input 3

1 1
2 1

Sample Output 3

0

Solution in Scala (2.11.7) (judge verdict: Accepted)


import scala.collection.mutable.PriorityQueue


object Main {

  def main(args: Array[String]): Unit = {

    val Array(n,m) = scala.io.StdIn.readLine().split(" ").map(_.toInt)

    val leftJobs = PriorityQueue.empty[(Int,Int)](Ordering.by[(Int,Int),Int](t => -t._1))
    val availables = PriorityQueue.empty[Int]

    (0 until n)
      .foreach(_ => {
        val Array(days,reward) = readLine().split(" ").map(_.toInt)
        leftJobs.enqueue(days -> reward)
      })

    val totalReward = (for { 
      leftDays <- 0 to m
    } yield {
      while(leftJobs.size > 0 && leftJobs.head._1 <= leftDays) {
        val v = leftJobs.dequeue()
        availables.enqueue(v._2)
      }

      if(availables.size == 0) {
        0
      } else {
        availables.dequeue()
      }
    }).sum

    println(totalReward)
  }

}