algorithm_2024/P4017/P4017.cpp

#include <iostream>
#include <ranges>
#include <queue>
#include <stdio.h>

using 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_TYPES], out_degree[MAX_TYPES], link_nums[MAX_TYPES], ans;
static std::queue<int> q;
static std::vector<int> next[MAX_TYPES];

class ReadInt{
    char c;
    int w,n;
public:
    ReadInt &operator>>(int &num){
        c=0,w=1,n=0;
        while(!isdigit(c)){
            if(c=='-')w=-1;
            c = (char)getchar();
        }
        while(isdigit(c)){
            n=n*10+(c-'0');
            c = (char)getchar();
        }
        num = n*w;
        return *this;
    }
};

static ReadInt readint;

#define cin readint

int main(){
    cin>>types>>rel_ships;
    for([[maybe_unused]] 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, types+1)){
        if(in_degree[i]==0){
            q.push(i);
            link_nums[i] = 1;
        }
    }

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

    for(auto i:range(1,types+1)){
        if(out_degree[i]==0){
            ans = (ans + link_nums[i]) % MOD;
        }
    }

    cout<<ans<<"\n";
}