Packaging Trap Problem
In fact, as long as one point is kept in the center, all other points can connect to other points in just two steps, while ensuring the minimum road.
//====================================================================||
// Name : Road Construction.cpp ||
// Date : 2013/7/20 10:13:31 PM ||
// 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);
}
}
}