Poj 2749 Building roads 2-sat

Poj 2749 Building roads 2-sat

Question:

To give the coordinates of n villages and the coordinates of two special points s1 and s2, connect each village to s1 or s2 to minimize the maximum distance between n villages.

Analysis:

2-sat is used to determine whether the maximum distance between any two villages is feasible. The answer can be recorded by the way when the two villages are separated, do not output l or l-1 when the last interval is null.

Code:

//poj 2749 //sep9#include 
 
  #include 
  
   using namespace std;const int maxN=1024;const int maxL=4000000;vector
   
     g[maxN],ng[maxN];int n,m,cnt,scc,vis[maxN],dfn[maxN]; int x1,y1,x2,y2;int x[maxN],y[maxN];int a,b;int ap[maxN],aq[maxN],bp[maxN],bq[maxN];int d[maxN],D;void addegde(int u,int v){g[u].push_back(v);ng[v].push_back(u);}void dfs(int k){vis[k]=1;for(int i=g[k].size()-1;i>=0;--i)if(!vis[g[k][i]])dfs(g[k][i]);dfn[++cnt]=k;}void ndfs(int k){vis[k]=scc;for(int i=ng[k].size()-1;i>=0;--i)if(!vis[ng[k][i]])ndfs(ng[k][i]);}void kosaraju(){memset(vis,0,sizeof(vis));cnt=0;for(int i=1;i<=2*n;++i)if(!vis[i])dfs(i);memset(vis,0,sizeof(vis));scc=0;for(int i=2*n;i>=1;--i)if(!vis[dfn[i]]){++scc;ndfs(dfn[i]);}}int two_sat(int dis){int i,j;for(i=1;i<=2*n;++i)g[i].clear(),ng[i].clear();for(i=1;i<=a;++i){int p=ap[i],q=aq[i];addegde(p,q+n);addegde(p+n,q);addegde(q,p+n);addegde(q+n,p); }for(i=1;i<=b;++i){int p=bp[i],q=bq[i];addegde(p,q);addegde(q,p);addegde(p+n,q+n);addegde(q+n,p+n);}for(i=1;i<=n;++i)for(j=i+1;j<=n;++j)if(i!=j){if(d[i]+d[j]>dis){addegde(i,j+n);addegde(j,i+n);}if(d[i]+d[j+n]+D>dis){addegde(j+n,i+n);addegde(i,j);}if(d[i+n]+d[j]+D>dis){addegde(i+n,j+n);addegde(j,i);}if(d[i+n]+d[j+n]>dis){addegde(i+n,j);addegde(j+n,i);}}kosaraju(); for(i=1;i<=n;++i)if(vis[i]==vis[i+n])return 0;return 1;}int main(){int i,j;scanf("%d%d%d",&n,&a,&b);scanf("%d%d%d%d",&x1,&y1,&x2,&y2);for(i=1;i<=n;++i)scanf("%d%d",&x[i],&y[i]);for(i=1;i<=n;++i){d[i]=abs(x[i]-x1)+abs(y[i]-y1);d[i+n]=abs(x[i]-x2)+abs(y[i]-y2);}D=abs(x1-x2)+abs(y1-y2);int p,q;for(i=1;i<=a;++i)scanf("%d%d",&ap[i],&aq[i]);for(i=1;i<=b;++i)scanf("%d%d",&bp[i],&bq[i]);int l=0,r=maxL,ans=-1; while(l