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| #include <bits/stdc++.h>
#define MAX_N 10001
#define ll long long
#define pll pair<ll, ll>
#define vpll vector<pll>
#define vll vector<ll>
#define all(a) begin(a), end(a)
using namespace std;
ll n, e;
bool vis1[MAX_N], vis2[MAX_N], vis3[MAX_N];
ll rep[MAX_N];
vll st;
void dfs1(ll u, vector<vll>& adj) {
vis1[u] = true;
for(auto& v : adj[u]) {
if(!vis1[v])
dfs1(v, adj);
}
st.push_back(u);
}
void dfs2(ll u, ll r, vector<vll>& radj) {
rep[u] = r;
vis2[u] = true;
for(auto& v : radj[u]) {
if(!vis2[v])
dfs2(v, r, radj);
}
}
vll solve(vpll& edges) {
vector<vll> adj(n + 1), radj(n + 1);
memset(vis1, 0, sizeof(vis1));
memset(vis2, 0, sizeof(vis2));
memset(vis3, 0, sizeof(vis3));
memset(rep, 0, sizeof(rep));
for(auto& [u, v]: edges) {
adj[u].push_back(v);
radj[v].push_back(u);
}
for(ll i = 1; i <= n; i++) {
if(!vis1[i])
dfs1(i, adj);
}
while(!st.empty()) {
ll u = st.back(); st.pop_back();
if(!vis2[u])
dfs2(u, u, radj);
}
unordered_set<ll> usll;
for(auto& [u, v] : edges) {
if(rep[u] == rep[v]) continue;
usll.insert(rep[u]);
}
vll res;
for(ll i = 1; i<= n; i++)
if(!usll.count(rep[i]))
res.push_back(i);
return res;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
while(true) {
cin>>n;
if(!n) break;
cin>>e;
ll u, v;
vpll edges;
while(e--) {
cin>>u>>v;
edges.push_back({u,v});
}
auto res = solve(edges);
for(auto& c : res) cout<<c<<' ';cout<<'\n';
}
return 0;
}
|
