Submission #2827286

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Source Code Expand

#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<iomanip>
#include<math.h>
#include<complex>
#include<queue>
#include<deque>
#include<map>
#include<set>
#include<bitset>
using namespace std;
#define REP(i,m,n) for(int i=(int)m ; i < (int) n ; i++ )
#define rep(i,n) REP(i,0,n)
typedef long long ll;
typedef pair<int,int> pint;
typedef pair<ll,int> pli;
const int inf=1e9+7;
const ll longinf=1LL<<60 ;
const ll mod=1e9+7 ;
int dx[4]={1,0,-1,0} , dy[4]={0,1,0,-1} ;

int main(){
   int n,m;
   cin>>n>>m;
   int a[m][2];
   rep(i,m){
       cin>>a[i][0]>>a[i][1];
       a[i][0]--;a[i][1]--;
   }
   bool ok[n];
   rep(i,n)ok[i]=true;
   vector<int> must[m][2];
   rep(i,n){
       bool used[n];
       rep(j,n)used[j]=false;
       used[i]=true;
       for(int j=m-1;j>=0;j--){
           if(used[a[j][0]]&&used[a[j][1]]){
               ok[i]=false;
               break;
           }
           if(used[a[j][0]]){
               used[a[j][1]]=true;
               must[j][1].push_back(i);
           }
           if(used[a[j][1]]){
               used[a[j][0]]=true;
               must[j][0].push_back(i);
           }
       }
   }
   bool check[n][n];
   rep(i,n)rep(j,n)check[i][j]=true;
   rep(i,m){
       for(auto x:must[i][0])for(auto y:must[i][1])
       check[x][y]=check[y][x]=false;
   }
   int ans=0;
   rep(i,n)REP(j,i+1,n){
       if(ok[i]&&ok[j]&&check[i][j])ans++;
   }
   cout<<ans<<endl;
   return 0;
}

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