Solution for Live Archive 6528 - Disjoint water supply

/*
 * 6528.cpp
 *
 *  Created on: Jul 30, 2014
 *      Author: ghooo
 */

#include <cstring>
#include <map>
#include <deque>
#include <queue>
#include <stack>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <vector>
#include <set>
#include <complex>
#include <list>
#include <climits>
#include <cctype>
#include <bitset>
//#include <windows.h>

using namespace std;

#define pb push_back
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define sz(v) ((ll)v.size())
#define rep(i,m) for(int i=0;i<(int)(m);++i)
#define rep2(i,n,m) for(int i=n;i<(int)(m);i++)
#define For(it,c) for(__typeof(c.begin()) it=c.begin();it!=c.end();++it)
#define reset(a,b) memset(a,b,sizeof(a))
#define mp make_pair
#define dot(a,b) ((conj(a)*(b)).X)
#define X real()
#define Y imag()
#define length(V) (hypot((V).X,(V).Y))
#define vect(a,b) ((b)-(a))
#define cross(a,b) ((conj(a)*(b)).imag())
#define normalize(v) ((v)/length(v))
#define rotate(p,about,theta) ((p-about)*exp(point(0,theta))+about)
#define pointEqu(a,b) (comp(a.X,b.X)==0 && comp(a.Y,b.Y)==0)
#define clrq(x) while(!x.empty()) x.pop();
#define clrvv(v) rep(i,sz(v))v[i].clear();
#define debug(x) cerr << #x << ": " << x << endl;
#define debugv(v) cerr << #v << ": ";For(it,v)cerr <<(*it)<<", "; cerr<<endl;

typedef stringstream ss;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<pii> vpii;
typedef vector<string> vs;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<vector<int> > vii;
typedef long double ld;
typedef complex<double> point;
typedef pair<point, point> segment;
typedef pair<double, point> circle;
typedef vector<point> polygon;
typedef unsigned long long ull;
typedef long long ll;

//==============================================================
// handling triples
typedef pair<ll,pair<ll,ll> > triple;
#define tfirst first
#define tsecond second.first
#define tthird second.second
#define mt(x,y,z) mp(x,mp(y,z))
//---------------------------------------------------------------

const int oo = (int) 1e9;
const double PI = 2 * acos(0.0);
const double eps = 1e-9;

vector<vector<int> > parents;
bool mem[1001][1001];
int vis[1001][1001],ID;
bool dp(int n1, int n2){
 if(n1 == n2) return n1 == 0;
 if(vis[n1][n2] == ID) return mem[n1][n2];
 vis[n1][n2] = ID;
 if(n1 > n2){
  rep(i,sz(parents[n1])){
   if(dp(parents[n1][i],n2)) return mem[n1][n2] = true;
  }
 } else {
  rep(i,sz(parents[n2])){
   if(dp(n1, parents[n2][i])) return mem[n1][n2] = true;
  }
 }
 return mem[n1][n2] = false;
}
int main(){
 ios_base::sync_with_stdio(false);
#ifndef ONLINE_JUDGE
 freopen("in.txt", "r", stdin);
 //freopen("out.txt", "w", stdout);
#endif
 int c, p;
 int u, v;
 while(cin >> c >> p){
  parents.clear();
  parents.resize(c);
  rep(i,p){
   cin >> u >> v;
   u--,v--;
   parents[max(u,v)].pb(min(u,v));
  }
  int ans = 0;
  ID++;
  rep(i,c){
   rep2(k,i+1,c){
    if(dp(i,k)) ans++;
   }
  }
  cout << ans << endl;
 }
 return 0;
}