稍微尝试了一下stl的vector和stack

#include <cstdio>#include <cstring>#include <vector>#include <stack>#include <iostream>#define maxn 10017using namespace std;int low[maxn],dfn[maxn],val[maxn],out[maxn];bool instack[maxn];int belong[maxn];int bcnt,index;int n,m;vector<int>g[maxn];stack<int>s;void init(){for (int i = 0; i < maxn; ++i)    {        g[i].clear();        low[i] = dfn[i] = belong[i] = val[i] = out[i] = 0;        instack[i] = false;    }    index = bcnt =0;}void tarjan(int i){int j,k;    low[i] = dfn[i] = ++index;    s.push(i);    instack[i] = true;for (k = 0; k < g[i].size(); ++k)    {        j = g[i][k];if (!dfn[j])        {            tarjan(j);            low[i] = min(low[i],low[j]);        }else if (instack[j])        {            low[i] = min(low[i],dfn[j]);        }    }if(low[i] == dfn[i])    {        bcnt++;do        {            j = s.top();            s.pop();            instack[j] = false;            belong[j] = bcnt;            val[bcnt]++;//记录缩点后的点真正拥有的点        } while (j != i);    }}void solve(){int count = 0,i,j;for (i = 1; i <= n; ++i)    {if (!dfn[i])  tarjan(i);    }for (i = 1; i <= n; ++i)    {for (j = 0; j < g[i].size(); ++j)        {int k = g[i][j];if (belong[i] != belong[k])out[belong[i]]++;        }    }int t = 0;for (i = 1; i <= bcnt; ++i)    {if (!out[i])        {            count++;            t = i;        }    }if (count > 1) puts("0");else    printf("%d\n",val[t]);}int main(){//freopen("d.txt","r",stdin);    int x,y,i;while (cin>>n>>m)    {        init();for (i = 1; i <= m; ++i)        {            cin>>x>>y;            g[x].push_back(y);        }        solve();    }return 0;}