To Bew

#include <cstdio>
#include <set>
#include <cstdlib>
#include <algorithm>

using namespace std;

typedef pair<int,int> II;
typedef set<II>::iterator iter;

int rand(int a, int b){
    return rand() % (b - a + 1) + a;
}

int main(){
    int n = 100000, m = 10000;
    set<II> used;
    for(int i = 0; i < m; ++i){
        while(true){
            int a = rand(1, n);
            int b = rand(1, n);
            if(a > b) swap(a, b);
            iter pos = used.lower_bound(II(a, b));
            if(pos != used.end() and *pos == II(a, b)){
                // we have generated this edge!
                // try again
            }else{
                printf("%d %d\n", a, b);
                used.insert(II(a, b));
                break;
            }
        }
    }
    return 0;
}