poj2553-The Bottom of a Graph（强连通分量）
The Bottom of a Graph
#include<stdio.h>#include<string.h>#include<vector>#include<stack>using namespace std;vector<int> vec[5005];stack<int> sta;int dfn[5005],low[5005];int vis[5005];int gro_id[5005],gro[5005];int now,id;int n,m;void tarjan(int s){ now++; vis[s]=2; dfn[s]=low[s]=now; sta.push(s); for(int i=0; i<vec[s].size(); i++) { if(vis[vec[s][i]]==0) { tarjan(vec[s][i]); low[s]=low[s]<low[vec[s][i]]?low[s]:low[vec[s][i]]; } else if(vis[vec[s][i]]==2) low[s]=low[s]<dfn[vec[s][i]]?low[s]:dfn[vec[s][i]]; } if(low[s]==dfn[s]) { id++; while(1) { int t=sta.top(); gro_id[t]=id; vis[t]=1; sta.pop(); gro[id]++; if(t==s) break; } }}int main(){ while(scanf("%d",&n)&&n!=0) { now=id=0; scanf("%d",&m); //printf("123\n"); memset(dfn,0,sizeof(dfn)); memset(low,0,sizeof(low)); memset(vis,0,sizeof(vis)); memset(gro_id,0,sizeof(gro_id)); memset(gro,0,sizeof(gro)); //printf("123\n"); for(int i=1; i<=n; i++) vec[i].clear(); for(int i=0; i<m; i++) { int a,b; scanf("%d%d",&a,&b); vec[a].push_back(b); } //printf("123\n"); for(int i=1; i<=n; i++) if(!vis[i]) tarjan(i); //printf("123\n"); memset(vis,0,sizeof(vis)); int s=0; for(int i=1; i<=n; i++) for(int j=0; j<vec[i].size(); j++) if(gro_id[i]!=gro_id[vec[i][j]]) { if(vis[gro_id[i]]==0) s++; vis[gro_id[i]]=1; } if(s!=id) { for(int i=1; i<=n; i++) { if(vis[gro_id[i]]==0) printf("%d ",i); } } printf("\n"); } return 0;}
