Problem:
Score : 400 points

Problem Statement

There are N pieces of sushi. Each piece has two parameters: "kind of topping" t_i and "deliciousness" d_i.
You are choosing K among these N pieces to eat.
Your "satisfaction" here will be calculated as follows:

The satisfaction is the sum of the "base total deliciousness" and the "variety bonus".

The base total deliciousness is the sum of the deliciousness of the pieces you eat.

The variety bonus is x*x, where x is the number of different kinds of toppings of the pieces you eat.

You want to have as much satisfaction as possible.
Find this maximum satisfaction.

Constraints

1 \leq K \leq N \leq 10^5

1 \leq t_i \leq N

1 \leq d_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N K
t_1 d_1
t_2 d_2
.
.
.
t_N d_N

Output

Print the maximum satisfaction that you can obtain.

Sample Input 1

5 3
1 9
1 7
2 6
2 5
3 1

Sample Output 1

26

If you eat Sushi 1,2 and 3:

The base total deliciousness is 9+7+6=22.

The variety bonus is 2*2=4.

Thus, your satisfaction will be 26, which is optimal.

Sample Input 2

7 4
1 1
2 1
3 1
4 6
4 5
4 5
4 5

Sample Output 2

25

It is optimal to eat Sushi 1,2,3 and 4.

Sample Input 3

6 5
5 1000000000
2 990000000
3 980000000
6 970000000
6 960000000
4 950000000

Sample Output 3

4900000016

Note that the output may not fit into a 32-bit integer type.

Solution in Rust (1.15.1) (judge verdict: Accepted)

// https://atcoder.jp/contests/abc116/tasks/abc116_d

use std::cell::RefCell;
#[allow(unused)]
use std::cmp::{max, min, Ord, Ordering, PartialOrd};
#[allow(unused)]
use std::collections::{BinaryHeap, HashMap, HashSet, VecDeque};
use std::io;
use std::io::{BufRead, Read, Write};
use std::str::FromStr;

struct Sushi {
    t: usize,
    d: usize,
}

fn calc(sum: usize, types: usize) -> usize {
    sum + types.pow(2)
}

#[allow(unused, non_snake_case)]
pub fn solve<R: BufRead, W: Write>(mut io: Io<R, W>) {
    let N: usize = io.next();
    let K: usize = io.next();

    // 美味しい順に K 個取ることを考える。これより評価値が高いのは種類数がより大きい場合しかあり得ない。
    // またこれより種類数が少ないケースは美味しさの総数も劣るので答えになりえない。
    // K+1 個目から最後の要素まで順番に見ていき、それが新しい種類であれば、
    // K 個のうち 2 つ以上あるものの中での最小のものと交換する。この時、この種類数において最大となっていると言える。
    // なぜなら、この種類の数を L とすると、これは全種類のうち最も美味しいものが一つずつ含まれていて、
    // それ以外全体の中から K+1-L 個美味しい順に選んでいるため。
    // よって、この操作を最後の要素まで繰り返すことで、最初に得たものより種類数が多い全ての場合の
    // ケースを網羅することができ、その最大値が答えとなる。

    let mut sushis = (0..N)
        .map(|_| {
            let t: usize = io.next();
            let d: usize = io.next();

            Sushi { t: t, d: d }
        })
        .vec();

    sushis.sort_by(|a, b| b.d.cmp(&a.d));

    // 各種類の最大のものは必ず選ばれ、以降取り出される必要はないから、そのタイプを Set で持つ。
    // 最大以外のものについては、最小のものが取り出されていくから、それらのみを含んだ priority queue で持つ。
    let mut added_types = RefCell::new(HashSet::new());
    let mut sum: usize = 0;
    let mut heap = BinaryHeap::new();

    for sushi in &sushis[0..K] {
        if !added_types.borrow().contains(&sushi.t) {
            added_types.borrow_mut().insert(&sushi.t);
        } else {
            heap.push(Reverse(sushi.d));
        }

        sum += sushi.d;
    }

    let mut res = calc(sum, added_types.borrow().len());

    let filtered = (&sushis[K..N])
        .iter()
        .filter(|sushi| !added_types.borrow().contains(&sushi.t));

    for sushi in filtered {
        let min = match heap.pop() {
            Some(Reverse(x)) => x,
            None => break,
        };

        sum = sum - min + sushi.d;
        added_types.borrow_mut().insert(&sushi.t);
        res = max(res, calc(sum, added_types.borrow().len()));
    }

    io.println(res);
}

#[allow(dead_code)]
fn main() {
    let stdin = io::stdin();
    let stdin_lock = stdin.lock();
    let stdout = io::stdout();
    let stdout_lock = stdout.lock();

    let io = Io {
        reader: stdin_lock,
        writer: stdout_lock,
    };

    solve(io);
}

/* IO helpers */

pub struct Io<R, W>
where
    R: BufRead,
    W: Write,
{
    pub reader: R,
    pub writer: W,
}

#[allow(dead_code)]
impl<R, W> Io<R, W>
where
    R: BufRead,
    W: Write,
{
    fn println<T: std::fmt::Display>(&mut self, value: T) {
        writeln!(&mut self.writer, "{}", value).expect("Unable to write");
    }

    fn print<T: std::fmt::Display>(&mut self, value: T) {
        write!(&mut self.writer, "{}", value).expect("Unable to write");
    }

    fn debug<T: std::fmt::Debug>(&mut self, value: T) {
        writeln!(&mut self.writer, "{:?}", value).expect("Unable to write");
    }

    fn next<T: FromStr>(&mut self) -> T {
        let token = self
            .reader
            .by_ref()
            .bytes()
            .map(|c| c.unwrap() as char)
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect::<String>();
        token.parse::<T>().ok().expect("Unable to parse")
    }

    fn nexts<T: FromStr>(&mut self, n: usize) -> Vec<T> {
        (0..n).map(|_| self.next::<T>()).collect::<Vec<T>>()
    }
}

/* Structure helpers */

trait IteratorExt: Iterator + Sized {
    fn vec(self) -> Vec<Self::Item> {
        self.collect()
    }
}

impl<T: Iterator> IteratorExt for T {}

#[derive(PartialEq, Eq, Debug, Copy, Clone, Default, Hash)]
pub struct Reverse<T>(pub T);

impl<T: PartialOrd> PartialOrd for Reverse<T> {
    #[inline]
    fn partial_cmp(&self, other: &Reverse<T>) -> Option<Ordering> {
        other.0.partial_cmp(&self.0)
    }

    #[inline]
    fn lt(&self, other: &Self) -> bool {
        other.0 < self.0
    }
    #[inline]
    fn le(&self, other: &Self) -> bool {
        other.0 <= self.0
    }
    #[inline]
    fn ge(&self, other: &Self) -> bool {
        other.0 >= self.0
    }
    #[inline]
    fn gt(&self, other: &Self) -> bool {
        other.0 > self.0
    }
}

impl<T: Ord> Ord for Reverse<T> {
    #[inline]
    fn cmp(&self, other: &Reverse<T>) -> Ordering {
        other.0.cmp(&self.0)
    }
}