Submission #1870578

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Source Code Expand

#define _USE_MATH_DEFINES
#include <iostream>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#include <utility>
#include <complex>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <deque>
#include <tuple>
#include <bitset>
#include <algorithm>
#include <random>
using namespace std;
typedef long double ld;
typedef long long ll;
typedef vector<int> vint;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef complex<ld> compd;
#define rep(i,n)	for(int i=0;i<n;i++)
#define srep(i,a,n)	for(int i=a;i<n;i++)
#define REP(i,n)	for(int i=0;i<=n;i++)
#define SREP(i,a,n)	for(int i=a;i<=n;i++)
#define rrep(i,n)	for(int i=n-1;i>=0;i--)
#define RREP(i,n)	for(int i=n;i>=0;i--)
#define all(a)	(a).begin(),(a).end()
#define mp(a,b)	make_pair(a,b)
#define mt	make_tuple
#define pb	push_back
#define fst	first
#define scn second
// #define bitcnt(x)	__builtin_popcountll(x)
int bitcnt(ll x) {
	x = ((x & 0xAAAAAAAAAAAAAAAA) >> 1) + (x & 0x5555555555555555);
	x = ((x & 0xCCCCCCCCCCCCCCCC) >> 2) + (x & 0x3333333333333333);
	x = ((x & 0xF0F0F0F0F0F0F0F0) >> 4) + (x & 0x0F0F0F0F0F0F0F0F);
	x = ((x & 0xFF00FF00FF00FF00) >> 8) + (x & 0x00FF00FF00FF00FF);
	x = ((x & 0xFFFF0000FFFF0000) >> 16) + (x & 0x0000FFFF0000FFFF);
	x = ((x & 0xFFFFFFFF00000000) >> 32) + (x & 0x00000000FFFFFFFF);
	return x;
}
int bitcnt(int x) {
	x = ((x & 0xAAAAAAAA) >> 1) + (x & 0x55555555);
	x = ((x & 0xCCCCCCCC) >> 2) + (x & 0x33333333);
	x = ((x & 0xF0F0F0F0) >> 4) + (x & 0x0F0F0F0F);
	x = ((x & 0xFF00FF00) >> 8) + (x & 0x00FF00FF);
	x = ((x & 0xFFFF0000) >> 16) + (x & 0x0000FFFF);
	return x;
}
// #define gcd(a, b)	__gcd__(a, b)
ll gcd(ll a, ll b) {
	return a%b == 0 ? b : gcd(b, a%b);
}
#define debug(x)	cout<<"case #" << x << ": " << endl
#define DEBUG 0
const ll inf = (ll)1e9;
const ll mod = 1e9 + 7;
const ld eps = 1e-9;
const int dx[] = { 0,1,0,-1 };
const int dy[] = { 1,0,-1,0 };

ll nglist[40];
int n, m;
vint edge[40];
int ret = 0;

void solve(int cur, ll state) {
	if (cur == n)	ret = max(ret, bitcnt(state));
	// 選択済み or 選べない
	else if (state&(1LL << cur)||state&nglist[cur])	solve(cur + 1, state);
	// 絶対に届かないので枝切り
	else if (bitcnt(state) + (n - cur) - bitcnt(state >> cur) < ret)	return;
	else {
		solve(cur + 1, state);
		solve(cur + 1, state ^ (1LL << cur));
	}
}

int main() {
	cin >> n >> m;
	rep(i, m) {
		int a, b;	cin >> a >> b;	a--;	b--;
		edge[a].push_back(b);
		edge[b].push_back(a);
		nglist[a] ^= (1LL << b);
		nglist[b] ^= (1LL << a);
	}
	ll state = 0;
	rep(i, n) {
		if (edge[i].size() == 0)	state ^= (1LL << i);
		else if (edge[i].size() == 1) {
			if (edge[edge[i][0]].size() > 1)	state ^= (1LL << i);
			else if (i > edge[i][0])	state ^= (1LL << i);
		}
	}
	solve(0, state);
	cout << ret << endl;
	return 0;
}

Submission Info

Judge Result