Submission #2548275

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Source Code Expand

#include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<unordered_map>
#include<unordered_set>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#include<cassert>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (Y);++(X))
#define reps(X,S,Y) for (int (X) = S;(X) < (Y);++(X))
#define rrep(X,Y) for (int (X) = (Y)-1;(X) >=0;--(X))
#define rreps(X,S,Y) for (int (X) = (Y)-1;(X) >= (S);--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()
#define eb emplace_back
#define UNIQUE(X) (X).erase(unique(all(X)),(X).end())
#define Endl endl

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T> using vv=vector<vector<T>>;
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"{"; rep(i,t.size()) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class T,size_t n> ostream& operator<<(ostream &os, const array<T,n> &t) {
	os<<"{"; rep(i,n) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T,class U> ostream& operator<<(ostream &os, const tuple<S,T,U> &t) { return os<<"("<<get<0>(t)<<","<<get<1>(t)<<","<<get<2>(t)<<")";}
template<class S, class T,class U,class V> ostream& operator<<(ostream &os, const tuple<S,T,U,V> &t) { return os<<"("<<get<0>(t)<<","<<get<1>(t)<<","<<get<2>(t)<<","<<get<3>(t)<<")";}
template<class T> inline bool MX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool MN(T &l,const T &r){return l>r?l=r,1:0;}
//#undef NUIP
#ifdef NUIP
#define out(args...){vector<string> a_r_g_s=s_p_l_i_t(#args, ','); e_r_r(a_r_g_s.begin(), args); }
vector<string> s_p_l_i_t(const string &s, char c){vector<string> v;int d=0,f=0;string t;for(char c:s){if(!d&&c==',')v.pb(t),t="";else t+=c;if(c=='\"'||c=='\'')f^=1;if(!f&&c=='(')++d;if(!f&&c==')')--d;}v.pb(t);return move(v);}
void e_r_r(vector<string>::iterator it) {}
template<typename T, typename... Args> void e_r_r(vector<string>::iterator it, T a, Args... args){ if(*it==" 1"||*it=="1") cerr<<endl; else cerr << it -> substr((*it)[0] == ' ', it -> length()) << " = " << a << ", "; e_r_r(++it, args...);}
#else
#define out
#endif
#ifdef __cpp_init_captures
template<typename T>vector<T> table(int n, T v){ return vector<T>(n, v);}
template <class... Args> auto table(int n, Args... args){auto val = table(args...); return vector<decltype(val)>(n, move(val));}
#endif
const ll MOD=1e9+7;
int re=0;
struct small_graph { // assume: |V| <= 64
  typedef unsigned long long state;
  int n;
  unordered_map<state, state> N; // neighbor of i
  small_graph(int n = 0) : n(n) { }
  void add_edge(int src, int dst) {
    n = max(n, max(src, dst)+1);
    N[1ull<<src] |= (1ull<<dst);
    N[1ull<<dst] |= (1ull<<src);
  }
  int maximal_cliques() {
    // enumerate cliques that include R, exclude X, arbitrary P.
    function<int (state,state,state)> rec = [&](state R, state P, state X) {
      if (!(P | X)) { // R is a bitset of maximal clique
        for (int i = 0; i < n; ++i, R >>= 1) 
          if (R & 1) cout << i << " ";
        cout << endl;
        return 1;
      }
      int count = 0;
      state u = (P | X); u = u & ~(u-1);
      while (P & ~N[u]) {
        state v = P & ~(P-1);
        count += rec(R | v, P & N[v], X & N[v]);
        P ^= v; X |= v;
      }
      return count;
    };
    return rec(0, (1ull<<n)-1, 0);
  }
  // independent set = clique in the complement graph
  int maximal_independent_set() {
    function<int (state,state,state)> rec = [&](state R, state P, state X) {
      if (!(P | X)) { // R is a bitset of maximal independent set
				MX(re,__builtin_popcountll(R));
				// out(R,1);
        // for (int i = 0; i < n; ++i, R >>= 1) 
        //   if (R & 1) cerr << i << " ";
        // cerr << endl;
        return 1; 
      }
      int count = 0;
      state u = (P | X); u = u & ~(u-1);
      while (P & (N[u]|u)) {
        state v = P & ~(P-1); 
        count += rec(R | v, P & ~(N[v]|v), X & ~(N[v]|v));
        P ^= v; X |= v;
      }
      return count;
    };
    return rec(0, (1ull<<n)-1, 0);
  }
};

int main(){
  ios_base::sync_with_stdio(false);
  cout<<fixed<<setprecision(0);
	int n,m;
	cin>>n>>m;
	small_graph g(n);
	rep(i,m){
		int x,y;
		cin>>x>>y; --x; --y;
		g.add_edge(x,y);
		// ex[x][y]=ex[y][x]=1;
	}
	g.maximal_independent_set();
	cout<<re<<endl;
	// rep(i,n)rep(j,i)if(!ex[i][j]) g.add_edge(i,j);
	// out(re,1);
	// cout<<re-(64-n)<<endl;
  return 0;
}

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