algorithm_2024/P4017/P4017.cpp

#include <iostream>
#include <ranges>
#include <queue>

using std::cin,std::cout,std::iostream;
static const constexpr auto range {std::ranges::views::iota};

static const constexpr int MOD {80112002}, MAX_TYPES {(int)5e3+5}, MAX_REL_SHIPS {(int)5e5+5};
static int types, rel_ships, a, b, in_degree[MAX_REL_SHIPS], out_degree[MAX_REL_SHIPS];
std::queue<int> q;
std::vector<int> next[MAX_REL_SHIPS];

int main(){
    iostream::sync_with_stdio(false);

    cin>>types>>rel_ships;
    for(const int _:range(1,rel_ships+1)){
        cin>>a>>b;
        next[a].push_back(b);
        in_degree[b]++;
        out_degree[a]++;
    }

    for(const int i:range(1, rel_ships+1)){
        if(in_degree[i]==0){
            q.push(i);
        }
    }

    while(q.empty()==false){
        auto front {q.front()};
        q.pop();
        for(auto i:next[front]){
            if(--in_degree[i]==0){
                q.push(i);
            }
        }
    }
}