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 Rust (1.15.1) (judge verdict: Accepted)


use std::io::*;
use std::str::FromStr;

pub fn read<T: FromStr>() -> T {
  let stdin = stdin();
  let stdin = stdin.lock();
  let token: String = stdin
    .bytes()
    .map(|c| c.expect("failed to read char") as char)
    .skip_while(|c| c.is_whitespace())
    .take_while(|c| !c.is_whitespace())
    .collect();
  token.parse().ok().expect("failed to parse token")
}

use std::cmp::{max, min};
use std::collections::BTreeMap;
use std::collections::BinaryHeap;

fn main() {
  let n = read::<i64>();
  let m = read::<i64>();
  // let mut map: BTreeMap<i64, BinaryHeap<i64>> = BTreeMap::new();
  let mut vec = vec![];

  for _ in 0..n {
    let a = read::<i64>();
    let b = read::<i64>();
    vec.push(vec![a, b]);
  }

  vec.sort_by(|a, b| a[0].cmp(&b[0]));
  let mut q = BinaryHeap::new();
  let mut idx = 0;
  let mut ans = 0;

  for k in 1..m + 1 {
    while idx < n && vec[idx as usize][0] <= k {
      q.push(vec[idx as usize][1]);
      idx += 1;
    }

    ans += match q.pop() {
      Some(b) => b,
      _ => 0,
    };

  }
  println!("{:?}", ans);

}