Trap Packaging Problem
In fact, as long as one point is in the center, all other points only need to be connected to other points in two steps, and it is guaranteed to have the minimum number of roads.
//====================================================================||
// Name : Road Construction.cpp ||
// Date : 2013/7/20 下午10:13:31 ||
// Author : GCA ||
// 6AE7EE02212D47DAD26C32C0FE829006 ||
//====================================================================||
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cctype>
#include <utility>
using namespace std;
#ifdef ONLINE\_JUDGE
#define ll "%lld"
#else
#define ll "%I64d"
#endif
typedef unsigned int uint;
typedef long long int Int;
#define Set(a,s) memset(a,s,sizeof(a))
#define Write(w) freopen(w,"w",stdout)
#define Read(r) freopen(r,"r",stdin)
#define Pln() printf("\\n")
#define I\_de(x,n)for(int i=0;i<n;i++)printf("%d ",x\[i\]);Pln()
#define De(x)printf(#x"%d\\n",x)
#define For(i,x)for(int i=0;i<x;i++)
#define CON(x,y) x##y
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\\
printf("%d ",dp\[htx\]\[hty\]);}Pln();}
#define M 1004
#define PII pair<int,int\>
#define PB push\_back
#define oo INT\_MAX
#define Set\_oo 0x3f
#define Is\_debug true
#define debug(...) if(Is\_debug)printf("DEBUG: "),printf(\_\_VA\_ARGS\_\_)
#define FOR(it,c) for(\_\_typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define eps 1e-6
bool xdy(double x,double y){return x>y+eps;}
bool xddy(double x,double y){return x>y-eps;}
bool xcy(double x,double y){return x<y-eps;}
bool xcdy(double x,double y){return x<y+eps;}
int min3(int x,int y,int z){
int tmp=min(x,y);
return min(tmp,z);
}
int max3(int x,int y,int z){
int tmp=max(x,y);
return max(tmp,z);
}
int n,m;
int mz\[M\]\[M\];
int con\[M\]\[M\];
bool canused\[M\];
int main() {
ios\_base::sync\_with\_stdio(0);
while(~scanf("%d%d",&n,&m)){
Set(con,0);
Set(mz,0);
for(int i=0;i<n;i++)canused\[i\]=1;
while(m--){
int x,y;
scanf("%d%d",&x,&y);
x--;y--;
canused\[x\]=canused\[y\]=0;
}
int index;
for(int i=0;i<n;i++){
if(canused\[i\]){
index=i;
}
}
printf("%d\\n",n-1);
for(int i=0;i<n;i++){
if(i==index)continue;
printf("%d %d\\n",i+1,index+1);
}
}
}