SMMR-153: Food Web

#include <bits/stdc++.h>
using namespace std;
int color[100001];
vector <int> g[100001];
bool cycle=false;
void dfs(int u){
    if(color[u]==1) {
        cycle=true;
        return ;
    }
    if(color[u]==2){
        return ;
    }
    color[u]=1;
    for(auto v:g[u]){
        dfs(v);
    }
    color[u]=2;
}
int main(){
    int n,m;
    scanf("%d %d",&n,&m);
    int head[n+1];
    vector <int> parent[n+1];

    for(int i=0;i<=n;i++){
        head[i]=0;
    }
    for(int i=1;i<=m;i++){
        int u,v;
        scanf("%d %d",&u,&v);
        g[v].push_back(u);
        parent[u].push_back(v);
        head[u]++;
    }


    for(int i=1;i<=n;i++){
        if(color[i]==0){
            dfs(i);
            if(cycle){
                printf("No");
                return 0;
            }
        }
    }

    printf("Yes\n");
    queue <int> q;
    vector <bool> visited(n+1,false);
    for(int i=1;i<=n;i++){//head[i]=0;
        if(head[i]==0) q.push(i);
    }
    while(!q.empty()){
        int u;
        u=q.front();
        q.pop();

        if(visited[u]) continue;
        bool con=true;
        for(auto pr:parent[u]){
            if(!visited[pr]) con=false;
        }

        if(con==false) continue;
        visited[u]=true;
        printf("%d ",u);
        for(auto v:g[u]){
            if(!visited[v]) {
                q.push(v);
            }
        }
    }


    return 0;
}