Language:Default Popular Cows
Description Input Output Sample Input 3 3 1 2 2 1 2 3 Sample Output 1 |
【题意】：
tarjia算法了解一下
https://www.byvoid.com/zhs/blog/scc-tarjan
https://blog.csdn.net/qq_34374664/article/details/77488976
AC代码：
#include<cstdio> #include<iostream> #include<cstring> #include<stack> #include<cmath> using namespace std; const int maxn=1e4+50; const int maxm=5e4+50; int head[maxn],LOW[maxn],DFN[maxn],id[maxn],cnt[maxn]; bool mark[maxn]; int N,M,time=0,scc=0; stack<int>sta; struct edge_t{ int to,next; }edge[maxm]; void init() { memset(head,-1,sizeof(head)); memset(DFN,0,sizeof(DFN)); memset(id,0,sizeof(id)); memset(cnt,0,sizeof(cnt)); memset(LOW,0,sizeof(LOW)); memset(mark,false,sizeof(mark)); } void tarjan( int u ) { DFN[u]=LOW[u]=++time; sta.push(u); mark[u]=true; for( int k=head[u]; k!=-1; k=edge[k].next ) { int v=edge[k].to; if(!DFN[v]) { tarjan(v); LOW[u]=min( LOW[u],LOW[v] ); } else if(mark[v]) { LOW[u]=min(LOW[u],DFN[v]); } } if(DFN[u]==LOW[u]) { scc++; int v; do { v=sta.top(); sta.pop(); id[v]=scc; mark[v]=false; cnt[scc]++; } while(u!=v); } } void solve() { for( int i=1; i<=N; i++ ) if(!DFN[i]) tarjan(i); memset(mark,0,sizeof mark); for( int i=1; i<=N; i++ ) { for( int k=head[i]; k!=-1; k=edge[k].next ) { if(id[i]!=id[edge[k].to]) mark[id[i]]=true; } } int pos=0,lab=0; for( int i=1; i<=scc; i++ )if(!mark[i]) { lab++; pos=i; } if(lab>1)printf("0\n"); else printf("%d\n",cnt[pos]); } int main() { init(); scanf("%d%d",&N,&M); for( int i=0; i<M; i++ ) { int a,b; scanf("%d%d",&a,&b); edge[i].to=b; edge[i].next=head[a]; head[a]=i; } solve(); return 0; }