#include <bits/stdc++.h>
using namespace std;
#define int long long
#define FOR(i,s,e) for(int i = s; i <= (int)e; ++i)
#define DEC(i,s,e) for(int i = s; i >= (int)e; --i)
#define IAMSPEED ios_base::sync_with_stdio(false); cin.tie(0);
#ifdef LOCAL
#define db(x) cerr << #x << "=" << x << "\n"
#define db2(x, y) cerr << #x << "=" << x << " , " << #y << "=" << y << "\n"
#define db3(a,b,c) cerr<<#a<<"="<<a<<","<<#b<<"="<<b<<","<<#c<<"="<<c<<"\n"
#define dbv(v) cerr << #v << ":"; for (auto ite : v) cerr << ite << ' '; cerr <<"\n"
#define dbvp(v) cerr << #v << ":"; for (auto ite : v) cerr << "{" << ite.f << ',' << ite.s << "} "; cerr << "\n"
#define dba(a,ss,ee) cerr << #a << ":"; FOR(ite,ss,ee) cerr << a[ite] << ' '; cerr << "\n"
#define reach cerr << "LINE: " << __LINE__ << "\n";
#else
#define reach
#define db(x)
#define db2(x,y)
#define db3(a,b,c)
#define dbv(v)
#define dbvp(v)
#define dba(a,ss,ee)
#endif
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define f first
#define s second
#define g0(x) get<0>(x)
#define g1(x) get<1>(x)
#define g2(x) get<2>(x)
#define g3(x) get<3>(x)
typedef pair <int, int> pi;
typedef tuple<int,int,int> ti3;
typedef tuple<int,int,int,int> ti4;
int rand(int a, int b) { return a + rng() % (b-a+1); }
const int MOD = 1e9 + 7;
const int inf = (int)1e9 + 500;
const long long oo = (long long)1e18 + 500;
template <typename T> bool chmax(T& a, const T b) { return a<b ? a = b, 1 : 0; }
template <typename T> bool chmin(T& a, const T b) { return a>b ? a = b, 1 : 0; }
const int MAXN = -1;
vector<int> V[1005];
int n,m;
int dist[1005];
pi bfs(int source) {
memset(dist,-1,sizeof dist);
queue<int> q;
dist[source]=0;
q.push(source);
while(q.size()) {
int x=q.front(); q.pop();
for(auto v:V[x]){
if(dist[v]==-1 || dist[v]>dist[x]+1) {
dist[v]=dist[x]+1;
q.push(v);
}
}
}
pi mx=pi(0,0);
FOR(i,1,n) {
chmax(mx,{dist[i],i});
}
return mx;
}
int dfs(int x, int p) {
int l=1;
for(auto v:V[x])if(v!=p) {
int res=dfs(v,x);
chmax(l,res+1);
}
return l;
}
int32_t main()
{
IAMSPEED
cin >> n >> m;
if(n==1) {
return cout << "YES\n1 \n1", 0;
} else if(n==2) {
return cout << "YES\n2 \n1 1", 0;
}
if(m!=(n-1)) return cout << "NO\n", 0; // cycle=cannot
/*
cout << "YES\n";
cout << 2*(n-2) << '\n';
FOR(i,2,n-1) cout << i << ' ';
DEC(i,n-1,2) cout << i << ' ';
*/
FOR(i,1,n-1){
int a,b; cin >> a >> b;
V[a].pb(b);
V[b].pb(a);
}
pi r=bfs(1);
int src=r.s;
int sink=bfs(src).s;
vector<int> path;
path.pb(sink);
while(path.back() != src) {
int x=path.back();
for(auto v:V[x]){
if(dist[v]==dist[x]-1){
path.pb(v);
break;
}
}
}
int S=path.size();
dbv(path);
if(S==2||S==3) {
return cout << "YES\n2 \n" << path[S/2] << ' ' << path[S/2], 0;
}
vector<int> ans;
ans.pb(path[1]);
FOR(i,2,path.size()-3) {
int x=path[i];
int pre=path[i-1];
int nxt=path[i+1];
vector<int> here;
for(auto v:V[x]) {
if(v==pre||v==nxt)continue;
db(v);
int l=dfs(v,x);
if(l>2) {
cout << "NO\n"; exit(0);
}
db(l);
if(l==2) {
here.pb(v);
} // if not, either of the iterations will cover it anyways?
}
ans.pb(x);
for(auto i:here) {
ans.pb(i);
ans.pb(x);
}
}
ans.pb(path[S-2]);
// now for the return.
ans.pb(path[S-2]);
DEC(i,path.size()-3,2) {
int x=path[i];
int pre=path[i+1];
int nxt=path[i-1];
vector<int> here;
for(auto v:V[x]) {
if(v==pre||v==nxt)continue;
int l=dfs(v,x);
db(l);
if(l>2) {
cout << "NO\n"; exit(0);
}
if(l==2) {
here.pb(v);
} // if not, either of the iterations will cover it anyways?
}
ans.pb(x);
for(auto i:here) {
ans.pb(i);
ans.pb(x);
}
}
ans.pb(path[1]);
cout << ans.size() << '\n';
for(auto i:ans)cout<<i<<' ';
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
340 KB |
Output is correct |
| 2 |
Correct |
0 ms |
340 KB |
Output is correct |
| 3 |
Incorrect |
0 ms |
340 KB |
Token "6" doesn't correspond to pattern "YES|NO" |
| 4 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
1 ms |
340 KB |
Output is correct |
| 2 |
Correct |
1 ms |
340 KB |
Output is correct |
| 3 |
Correct |
0 ms |
340 KB |
Output is correct |
| 4 |
Incorrect |
1 ms |
348 KB |
Token "4" doesn't correspond to pattern "YES|NO" |
| 5 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
340 KB |
Output is correct |
| 2 |
Correct |
0 ms |
340 KB |
Output is correct |
| 3 |
Incorrect |
0 ms |
340 KB |
Token "6" doesn't correspond to pattern "YES|NO" |
| 4 |
Halted |
0 ms |
0 KB |
- |
