POJ_1236 强连通分支

http://poj.org/problem?id=1236

#include <iostream>#include <string.h>#include <stack>#define MAX 101using namespace std;int n,g[MAX][MAX],tmp,in[MAX],out[MAX];int dfn[MAX],low[MAX],index=1,cnt=0,belong[MAX];bool instack[MAX];stack<int> Q;int min(int a,int b){return a<b?a:b;}int max(int a,int b){return a>b?a:b;}void init(){memset(g,0,sizeof(g));memset(instack,false,sizeof(instack));cin>>n;for (int i=1;i<=n;i++)//建图while (1) {cin>>tmp;if (tmp==0) break;g[i][tmp]=true;}}void tarjan(int x)//求连通分支{dfn[x]=low[x]=index;index++;Q.push(x);instack[x]=true;for (int i=1;i<=n;i++) {if (!g[x][i]) continue;if (!dfn[i]) {tarjan(i);low[x]=min(low[x],low[i]);}else if (instack[i])low[x]=min(low[x],dfn[i]);}if (low[x]==dfn[x]) { cnt++; while (1) {tmp=Q.top();Q.pop();belong[tmp]=cnt;instack[tmp]=false;if (tmp==x) break;}}}void q2(){int ans1=0,ans2=0,i,j;for (i=1;i<=n;i++)for (j=1;j<=n;j++) //对于强连通分支缩点，并算出入度与出度{if (!g[i][j]) continue;if (belong[i]!=belong[j]) { in[belong[j]]++; out[belong[i]]++;}}for (i=1;i<=cnt;i++) {if (!in[i]) ans1++;if (!out[i]) ans2++;}if (cnt==1) cout<<1<<endl<<0<<endl;else cout<<ans1<<endl<<max(ans1,ans2)<<endl;}void display(){init();for (int i=1;i<=n;i++)if (!dfn[i])tarjan(i);q2();}int main(){ // freopen("in.txt","r",stdin); display(); return 0;}