This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long long ll;
const int N=100005,INF=1e9;
struct DSU{
int p[N],sz[N];
void init(int n){
iota(p,p+n+1,0);
fill(sz,sz+n+1,1);
}
int Find(int u){
return (p[u]==u?u:p[u]=Find(p[u]));
}
bool operator()(int u,int v){
u=Find(u);v=Find(v);
if(u==v)return 0;
if(sz[u]>sz[v])swap(u,v);
sz[v]+=sz[u];
p[u]=v;
return 1;
}
}dsu;
int n,root,special;
int dp[N][2][2][2][2];//cur,root,par,special
int p[N];
vector<vector<int>>adj(N);
void dfs(int v,int par){
p[v]=par;
for(auto u:adj[v]) {
if(u==par)continue;
dfs(u,v);
}
}
int solve(int v,int cur,int par,int rot,int sp){
int&ret=dp[v][cur][par][root][sp];
if(~ret)return ret;
ret=INF;
bool flag=1;
if(v==root&&cur!=rot)flag=0;
if(v==special&&cur!=sp)flag=0;
if(v==special&&par&&rot)flag=0;
if(!flag)return ret;
bool covered=0;
if(par)covered=1;
if(v==root&&sp)covered=1;
if(v==special&&rot)covered=1;
ll sum=cur;
for(auto u:adj[v]){
if(u==p[v])continue;
sum+=solve(u,0,cur,rot,sp);
}
if(covered){
ret=min(ll(ret),sum);
}else{
for(auto u:adj[v]){
if(u==p[v])continue;
ll val=sum-solve(u,0,cur,rot,sp)+solve(u,1,cur,rot,sp);
ret=min(ll(ret), val);
}
}
return ret;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
memset(dp,-1,sizeof(dp));
cin>>n;
dsu.init(n);
for(int i=0;i<n;i++){
int u,v;
cin>>u>>v;
if(!dsu(u,v)){
root=u;
special=v;
}else{
adj[u].push_back(v);
adj[v].push_back(u);
}
}
dfs(root,0);
int res=INF;
for(auto rot:{0,1})for(auto sp:{0,1})res=min(res,solve(root,rot,0,rot,sp));
cout<<(res==INF?-1:res);
return 0;
}
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