Submission #500798

#	Time	Username	Problem	Language	Result	Execution time	Memory
500798		pancankes	Knapsack (NOI18_knapsack)	C++17	Compilation error	0 ms	0 KiB

knapsack

#include <iostream>
#include <vector>
#include <set>
#include <map>
using namespace std;
#define ll long long

const int MAXN=1e5+2;
const int MOD=1e9+7;

int main()
{
    ll s,n;
    cin >> s >> n;
    // since s<=2000, and n<=1000000
    // there will inevitably be repeated weights, so we can group them together
    map<int, vector<pair<int,int> > >weights; 
    for (int i=0; i<n; i++)
    {
        int p,w,n;
        cin >> p >> w >> n;
        weights[w].push_back({p,n});
    }
    vector<vector<int>> dp(weights.size()+1,vector<int>(s+1,0));
    dp[0][0]=0;
    int at=1;
    for (auto& [w, items] : weights)
    {
        sort(items.rbegin(),items.rend());
        for (int i=0; i<=s; i++)
        {
            dp[at][i]=dp[at-1][i];
            int copies=0, j=0, cur=0;
            ll profit=0;

            // while there are items and while it is within the usable weight
            // we can use copies since all groups of items are of the same weight
            while ((copies+1) * w <= i && j<items.size())
            {
                copies++;
                profit+=items[j].first;
                dp[at][i]=max((ll)dp[at][i],dp[at-1][i-copies*w]+profit);
                cur++;
                if (cur==items[j].second)
                {
                    cur=0;
                    j++;
                }
            } 
        }
        at++;
    }
    // max_element gives a ptr to the value of the max element in a vector
    cout << *max_element(dp.back().begin(),dp.back().end()) << endl;
}

Compilation message (stderr)

knapsack.cpp: In function 'int main()':
knapsack.cpp:29:9: error: 'sort' was not declared in this scope; did you mean 'qsort'?
   29 |         sort(items.rbegin(),items.rend());
      |         ^~~~
      |         qsort
knapsack.cpp:38:44: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |             while ((copies+1) * w <= i && j<items.size())
      |                                           ~^~~~~~~~~~~~~
knapsack.cpp:54:14: error: 'max_element' was not declared in this scope
   54 |     cout << *max_element(dp.back().begin(),dp.back().end()) << endl;
      |              ^~~~~~~~~~~