Poj 1236 -- network of schools

Tarjan Algorithm

Note: For a strongly connected graph, the output value is 0 1.

Point reduction using the Tarjan algorithm.

The first question is the number of input points = 0.

The number of edges added in the second question is max (number of inbound vertex = 0, and number of outbound vertex = 0 ). Now let's write down the theorem.

#include<iostream>#include<cstdio>#include<cstring>using namespace std;#define maxm 21000#define maxn 220int n;int head[maxn],cnt;int v[maxm],next[maxm];int dfn[maxn],low[maxn],step;int sta[maxn],top;int ID[maxn],IdNum;int d_in[maxn],d_out[maxn];bool vis[maxn];void add(int a,int b){v[cnt]=b;next[cnt]=head[a];head[a]=cnt++;}void Init(){memset(vis,0,sizeof(vis));memset(d_in,0,sizeof(d_in));memset(d_out,0,sizeof(d_out));memset(head,-1,sizeof(head));memset(dfn,0,sizeof(dfn));memset(low,0,sizeof(low));IdNum=top=step=cnt=0;}void tarjan(int u){low[u]=dfn[u]=++step;sta[++top]=u;vis[u]=1;for(int i=head[u];~i;i=next[i]){int to=v[i];if(!dfn[to]){tarjan(to);low[u]=min(low[u],low[to]);}elseif(vis[to])low[u]=min(low[u],dfn[to]);}if(low[u]==dfn[u]){int x;IdNum++;do{x=sta[top--];vis[x]=0;ID[x]=IdNum;}while(u!=x);}}void build(){for(int i=1;i<=n;i++)for(int j=head[i];~j;j=next[j]){int to=v[j];if(ID[i]!=ID[to]){d_in[ID[to]]++;d_out[ID[i]]++;}}}int main(){int x;while(~scanf("%d",&n)){Init();for(int i=1;i<=n;i++){scanf("%d",&x);while(x){add(i,x);scanf("%d",&x);}}for(int i=1;i<=n;i++)if(!dfn[i])tarjan(i);build();int ans1=0;int ans2=0;for(int i=1;i<=IdNum;i++){if(d_in[i]==0)ans1++;if(d_out[i]==0)ans2++;}if(IdNum!=1)printf("%d\n%d\n",ans1,max(ans1,ans2));elseprintf("1\n0\n");}return 0;}