蓝题训练9.25P2962 [USACO09NOV] Lights G

P2962 [USACO09NOV] Lights G
https://www.luogu.com.cn/problem/P7323
Tag：略
题意：略

题解：meet in the middle第一次见

参考代码

#include<bits/stdc++.h>
using namespace std;
using ll =long long;
ll n,m;
ll f[1000005],g[1000005],ans[40];
vector<ll> a[40];
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cin>>n>>m;
	ans[0]=1;
	for(int i=1;i<=38;i++){
		ans[i]=ans[i-1]*2;
	}
	for(ll x,y, i=1;i<=m;i++){
		cin>>x>>y;
		a[x].push_back(y);
		a[y].push_back(x);
	}
	ll s=n/2,t=n-s;
	ll now=0;
	f[0]=0;
	for(ll i=1;i<((1LL<<(s)));i++){
		if(__builtin_popcount(i)==1){
			now++;
			f[i]+=ans[now-1];
			for(auto j:a[now]){
				f[i]+=ans[j-1];
			}
		}
		else{
			ll u=(i&-i);
			f[i]=f[i-u]^f[u];
		}
	}
	g[0]=0;
	for(ll i=1;i<((1LL<<(t)));i++){
		if(__builtin_popcount(i)==1){
			now++;
			g[i]+=ans[now-1];
			for(auto j:a[now]){
				g[i]+=ans[j-1];
			}
		}
		else{
			ll u=(i&-i);
			g[i]=g[i-u]^g[u];
		}
	}
	map<ll,ll> mp;
	for(ll i=0;i<((1LL<<(s)));i++){
		f[i]^=((1LL<<(n))-1);
		if(mp.find(f[i])!=mp.end()) mp[f[i]]=min(mp[f[i]],(ll)__builtin_popcount(i));
		else mp[f[i]]=(ll)__builtin_popcount(i);
	}
	ll v=n+8;
	for(ll i=0;i<((1LL<<(t)));i++){
		if(mp.find(g[i])!=mp.end()) v=min(v,(ll)__builtin_popcount(i)+mp[g[i]]);
	}
	cout<<v<<"\n";
	return 0;
}

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