#include

#include

#include

using namespace std;

int main() {

int n;

cin >> n;




vector<vector<int>> v;


for(int i=0; i<n; i++){

    int a, b;
    
    cin >> a >> b;
    
    v.push_back({a, b});
    
}

sort(v.begin(), v.end());
vector<vector<int>> ans;
int start = v[0][0], end = v[0][1];


for(int i=1; i<n; i++){
    if(v[i][0] <= end){ 
        if(v[i][1] > end) end = v[i][1];
    } else {  
        ans.push_back({start, end});  
        start = v[i][0];
        end = v[i][1];
    }
}
ans.push_back({start, end});  
cout << ans.size() << endl;
for(auto x: ans){
    cout << x[0] << " " << x[1] << endl;
}

return 0;

}

#include <bits/stdc++.h> using namespace std; const int Maxn=5010; struct Node{ int x,y; }a[Maxn]; int n,cnt=0,last; bool cmp(const Node & t1,const Node & t2){ return t1.x<t2.x; } int main() { cin>>n; for(int i=1;i<=n;i++){ cin>>a[i].x; cin>>a[i].y; } sort(a+1,a+n+1,cmp); last=a[1].y; cnt+=1; for(int i=2;i<=n;i++){ if(a[i].x<=last){ last=max(last,a[i].y); }else{ a[cnt].y=last; last=a[i].y; cnt+=1; a[cnt].x=a[i].x;} } a[cnt].y=last; cout<<cnt<<endl; for(int i=1;i<=cnt;i++){ cout<<a[i].x<<" "<<a[i].y<<endl; } return 0; }

#include <bits/stdc++.h> using namespace std; const int Maxn=5010; struct Node{ int x,y; }a[Maxn]; int n,cnt=0,last; bool cmp(const Node & t1,const Node & t2){ return t1.x<t2.x;} int main() { cin>>n; for(int i=1;i<=n;i++){ cin>>a[i].x; cin>>a[i].y; } sort(a+1,a+n+1,cmp); last=a[1].y; cnt+=1; for(int i=2;i<=n;i++){ if(a[i].x<=last){ last=max(last,a[i].y); }else { a[cnt].y=last; last=a[i].y; cnt+=1; a[cnt].x=a[i].x; } } a[cnt].y=last; cout<<cnt<<endl; for(int i=1;i<=cnt;i++){ cout<<a[i].x<<" "<<a[i].y<<endl; } return 0; }

#include<bits/stdc++.h>
using namespace std;
int l[1000000],r[1000000],p[10000],n,L=-999,R=-9999,k,o=0,sum=1;int main() {cin>>n;for(int i=0; i<n; i++) cin>>l[i]>>r[i];for(int i=0; i<n-1; i++) {k=i;for(int j=i+1; j<n; j++) if(l[k]>l[j])k=j;if(k!=i) {swap(l[i],l[k]);swap(r[i],r[k]);}}L=l[0];R=r[0];for(int i=1; i<n; i++) {if(l[i]<=R)if(r[i]>R) {R=r[i];}if(l[i]>R) {sum++;p[++o]=L;p[++o]=R;L=l[i];R=r[i];}}o=1;cout<<sum<<endl;for(int i=1; i<sum; i++) {cout<<p[o]<<" "<<p[o+1]<<endl;o+=2;}cout<<L<<" "<<R;}

哇，居然只有三行！我就抄这个了！

就不再考虑优化了，随便贴出来吧，一个比较麻烦的方法，不过这个解法就算是把测试点继续强化也不怕了

using namespace std;
int u=0,n,a[131452],b,c,m,cot=0,maxn,mina[1000],maxa[1000],p=1145141,mi[10000],cache,ma[10000];
int main() {
	cin>>n;
	for(int i=0; i<n; i++) {
		cin>>b>>c;
		if(b<p) p=b;
		if(c>maxn) maxn=c;
		for(int j=b+1000; j<=c+1000; j++) a[j]=1;
		mi[i]=b+1000,ma[i]=c+1000;
	}
	for(int i=p+1000; i<=maxn+1000; i++) {
		if(a[i]==0) cache++;
		int iq=-1132,iw=-54154,ip=0;
		for(int j=0; j<n; j++) {
			if(mi[j]==i) 
				iq=mi[j];
			if(ma[j]<i&&ma[j]>iw) 
				iw=ma[j],u=j;
		}
		for(int j=0; j<n; j++) {
			if((mi[j]<i&&ma[j]>=i)||(mi[j]<=i&&ma[j]>i)) 
				ip=1;
		}
		if(a[i]!=0&&a[i-1]==1) {
			ip=0;
			for(int j=0; j<n; j++) {
				if((mi[j]<mi[u]&&ma[j]>=ma[u])||(mi[j]<=mi[u]&&ma[j]>ma[u])) {
					ip=1;
					break;
				}
			}
			if(i-1==iw&&i==iq&&ip==0) {
				maxa[cot]-=cache;
				cache=0,cot++,mina[cot]=i-1000;
			}
		}
		else if((a[i]!=0&&a[i-1]==0)) {
			bool rtx=false;
			for(int o=0; o<n; o++) 
				if(i>=mi[o]&&i<=ma[o]) rtx=true;
			if(rtx==true) {
				maxa[cot]-=cache;
				cache=0;
				cot++;
				if((a[i]!=0&&a[i-1]==0)||(a[i]!=0&&i==p+1000)) mina[cot]=i-1000;
			}
		} 
		if(maxa[cot]<i) maxa[cot]=i-1000;
	}
	cout<<cot<<endl;
	for(int i=1; i<=cot; i++) 
		cout<<mina[i]<<" "<<maxa[i]<<endl;
	return 0;
}

#include<bits/stdc++.h>
using namespace std;
int l[1000000],r[1000000],p[10000];
int main()
{
	int n,L=-999,R=-9999,k,o=0,sum=1;
	cin>>n;
	for(int i=0;i<n;i++)
	{
		cin>>l[i]>>r[i];
	}
	for(int i=0;i<n-1;i++)
	{
		k=i;
		for(int j=i+1;j<n;j++)
		{
			if(l[k]>l[j])k=j;
		}
		if(k!=i)
		{
			swap(l[i],l[k]);
			swap(r[i],r[k]);
		}
	}
	L=l[0];
	R=r[0];
	for(int i=1;i<n;i++)
	{
		if(l[i]<=R)
		{
			if(r[i]>R)
			{
				R=r[i];
			}
		}
		if(l[i]>R)
		{
			sum++;
			p[++o]=L;
			p[++o]=R;
			L=l[i];
			R=r[i];
		}
	}
	o=1;
	cout<<sum<<endl;
	for(int i=1;i<sum;i++)
	{
		cout<<p[o]<<" "<<p[o+1]<<endl;
		o+=2;
	}
	cout<<L<<" "<<R;
}

#include <bits/stdc++.h> using namespace std; const int Maxn=5010; struct Node( int x,y; ); Node a[Maxn]; bool cmp(const Node &t1,const Node &t2){ return t1.x<t2.x; } int n,cnt=0,last=0; int main() { cin>>n; for(int i=1; i<=n;i++){ cout<<a[i].x<<a[i].y<<endl; } last=a[1].y; cnt=1; for(int i=2;i<=n;i++){ if (a[i].x<=last){ last=max(last,a[i].y); }else{ a[cnt].y=last; cin+=1; a[cnt].x=a[i].x; last=a[i].y } } a[cnt].y=last; cout<<cnt<<endl; for(int i=1;i<=cnt.i++){ cout<<a[i],x<<" "<<a[i].y<<endl; } return 0; }