Queue

#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>
 
const int M = 2000;
const int N = 1e5;
const long long inf = 1e18;
std::vector<int> members [M];
int fit[M+1]; // How many people from groups 1..i can be fitted to one bus?
 
int main() {
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(0);
 
	int n, m, k;
	std::cin >> n >> m >> k;
	// Time, size
	std::vector<std::pair<int, int>> groups;
	for (int i = 0; i < n; ++i) {
		int a;
		std::cin >> a;
		members[a-1].push_back(i+1);
	}
	for (int i = 0; i < m; ++i) {
		if (! members[i].empty()) {
			groups.push_back({members[i][members[i].size()-1], members[i].size()});
		}
	}
	std::sort(groups.begin(), groups.end());
	/*
	for (int i = 0; i < groups.size(); ++i) {
		std::cout << groups[i].first << ' ' << groups[i].second << '\n';
	}
	*/
	fit[0] = 0;
	for (int i = 1; i <= m; ++i) {
		for (int j = 0; j < i; ++j) {
			if (fit[j] + groups[i-1].second <= k) {
				fit[i] = std::max(fit[i], fit[j] + groups[i-1].second);
			}
		}
		//std::cout << fit[i] << '\n';
	}
 
	long long cost = inf;
	for (int i = groups.size()-2; i >= 0; --i) {
		int first = fit[i+1];
		int second = n - fit[i+1];
		if (second <= k) {
			cost = std::min(cost, first * (long long) groups[i].first + second * (long long) n);
		}
	}
	if (n <= k) {
		cost = std::min(cost, n * (long long)n);
	}
	if (cost == inf) {
		std::cout << "-1\n";
	} else {
		std::cout << cost << '\n';
	}
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED

Test 31

Verdict: ACCEPTED

Test 32

Verdict: ACCEPTED

Test 33

Verdict: ACCEPTED

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED

Test 36

Verdict: ACCEPTED

Test 37

Verdict: ACCEPTED

Test 38

Verdict: ACCEPTED

Test 39

Verdict: ACCEPTED

Test 40

Verdict: ACCEPTED

Test 41

Verdict: ACCEPTED

Test 42

Verdict: ACCEPTED

Test 43

Verdict: ACCEPTED

Test 44

Verdict: ACCEPTED

Test 45

Verdict: ACCEPTED

Test 46

Verdict: ACCEPTED

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: ACCEPTED

Test 51

Verdict: ACCEPTED

Test 52

Verdict: ACCEPTED

Test 53

Verdict: ACCEPTED

Test 54

Verdict: ACCEPTED

Test 55

Verdict: ACCEPTED

Test 56

Verdict: ACCEPTED

Test 57

Verdict: ACCEPTED

Test 58

Verdict: ACCEPTED

Test 59

Verdict: ACCEPTED

Test 60

Verdict: ACCEPTED