#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
vector<pair<ll,ll> >vp;
ll uset[200005];
ll find(ll x)
{
ll p=x,t;
while(uset[p]!=p)p=uset[p];
while(x!=uset[x])
{
t=uset[x];
uset[x]=p;
x=t;
}
return x;
}
void unionset(ll x,ll y)
{
if((x=find(x)) == (y=find(y)) )return;
uset[x]=y;
}
void solve()
{
vp.clear();
int n,m,deg[100005]={
};
cin>>n>>m;
for(int i=1;i<=2*n;i++)uset[i]=i;
for(int i=1;i<=m;i++)
{
ll c,d;
cin>>c>>d;
unionset(c,d+n);
deg[c]++;
deg[d+n]++;
}
int l=1,r=1;
int res=-1,flag=0;
queue<int> q;
for(int i=1;i<=2*n-m;i++)
{
if(flag==1)r=res;
flag=0;
while(deg[l]==2)l++;
if(i==2*n-m){
for(int k=1;k<=n;k++)if(deg[k]==1)l=k;for(int j=n+1;j<=2*n;j++)if(deg[j]==1)r=j-n;}
else
{
while((find(l)==find(r+n)||deg[r+n]==2))
{
if(find(l)==find(r+n) && deg[r+n]!=2 && flag==0){
res=r;flag=1;}
r++;
}
unionset(l,r+n);
}
vp.push_back(make_pair(l,r));
deg[l]++;
deg[r+n]++;
}
cout<<vp.size()<<endl;
for(int i=0;i<vp.size();i++)
{
cout<<vp[i].first<<' '<<vp[i].second<<endl;
}
}
int main(){
ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
int T;
cin>>T;
for(int i=1;i<=T;i++)solve();
}
CCPC2021网络赛重赛 1010 Bigraph Extension
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Origin blog.csdn.net/Ambrumf/article/details/120691277
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