【2-sat】Gym - 101201F - Illumination

#include<cstdio>
#include<cstring>
#include<vector>
using namespace std;
vector<int>G[2005],rG[2005],vs;
int a[1005][1005];
int n,r,l,xs[1005],ys[1005];
void AddEdge(int U,int V){
	G[U].push_back(V);
	rG[V].push_back(U);
}
bool used[2005];
void dfs(int U){
	used[U]=1;
	for(int i=0;i<G[U].size();++i){
		if(!used[G[U][i]]){
			dfs(G[U][i]);
		}
	}
	vs.push_back(U);
}
int K,cmp[2005];
void rdfs(int U){
	used[U]=1;
	cmp[U]=K;
	for(int i=0;i<rG[U].size();++i){
		if(!used[rG[U][i]]){
			rdfs(rG[U][i]);
		}
	}
}
int main(){
//	freopen("f.in","r",stdin);
	scanf("%d%d%d",&n,&r,&l);
	for(int i=1;i<=l;++i){
		scanf("%d%d",&xs[i],&ys[i]);
		a[xs[i]][ys[i]]=i;
	}
	for(int i=1;i<=l;++i){
		for(int j=1;j<=2*r && xs[i]+j<=n;++j){
			if(a[xs[i]+j][ys[i]]){
				AddEdge(i,a[xs[i]+j][ys[i]]+l);
			}
		}
		for(int j=1;j<=2*r && xs[i]-j>=1;++j){
			if(a[xs[i]-j][ys[i]]){
				AddEdge(i,a[xs[i]-j][ys[i]]+l);
			}
		}
		for(int j=1;j<=2*r && ys[i]+j<=n;++j){
			if(a[xs[i]][ys[i]+j]){
				AddEdge(i+l,a[xs[i]][ys[i]+j]);
			}
		}
		for(int j=1;j<=2*r && ys[i]-j>=1;++j){
			if(a[xs[i]][ys[i]-j]){
				AddEdge(i+l,a[xs[i]][ys[i]-j]);
			}
		}
	}
	for(int i=1;i<=2*l;++i){
		if(!used[i]){
			dfs(i);
		}
	}
	memset(used,0,sizeof(used));
	for(int i=vs.size()-1;i>=0;--i){
		if(!used[vs[i]]){
			++K;
			rdfs(vs[i]);
		}
	}
	for(int i=1;i<=l;++i){
		if(cmp[i]==cmp[i+l]){
			puts("NO");
			return 0;
		}
	}
	puts("YES");
	return 0;
}