Submission #673804

#	Time	Username	Problem	Language	Result	Execution time	Memory
673804		ThinGarfield	Knapsack (NOI18_knapsack)	C++11	100 / 100	153 ms	35148 KiB

knapsack

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define mp make_pair
#define F first
#define S second

int main() {
  int limit;
  int type_num;
  cin >> limit >> type_num;

  // grouping elements by weight
  map<int, vector<pair<int, int>>> by_weight;
  for (int t = 0; t < type_num; t++) {
    int value;
    int weight;
    int amt;
    cin >> value >> weight >> amt;
    amt = min(amt, limit / weight);
    if (weight <= limit && amt > 0) {
      by_weight[weight].push_back({value, amt});
    }
  }

  /*
   * best[i][j] contains the most value we can
   * get using j weight and the first i weight types
   */
  vector<vector<long long>> best(by_weight.size() + 1, vector<long long>(limit + 1, INT32_MIN));
  best[0][0] = 0;
  int at = 1;
  for (auto& [w, items] : by_weight) {
    // sort items of given weight in reverse order by value
    sort(items.rbegin(), items.rend());
    for (int i = 0; i <= limit; i++) {
      best[at][i] = best[at - 1][i];
      int copies = 0;
      int type_at = 0;
      int curr_used = 0;
      long long profit = 0;
      // go through as many items until we run out of items or usable weight
      while ((copies + 1) * w <= i && type_at < items.size()) {
        copies++;
        profit += items[type_at].first;
        if (best[at - 1][i - copies * w] != INT32_MIN) {
          best[at][i] = max(best[at][i], best[at - 1][i - copies * w] + profit);
        }

        curr_used++;
        if (curr_used == items[type_at].second) {
          curr_used = 0;
          type_at++;
        }
      }
    }
    at++;
  }
  cout << *max_element(best.back().begin(), best.back().end()) << endl;
}

Compilation message (stderr)

knapsack.cpp: In function 'int main()':
knapsack.cpp:34:14: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
   34 |   for (auto& [w, items] : by_weight) {
      |              ^
knapsack.cpp:44:47: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   44 |       while ((copies + 1) * w <= i && type_at < items.size()) {
      |                                       ~~~~~~~~^~~~~~~~~~~~~~

• Subtask 1: 12 / 12
• Subtask 2: 17 / 17
• Subtask 3: 20 / 20
• Subtask 4: 24 / 24
• Subtask 5: 27 / 27