hdu 2647 bfs+拓撲排序

#include<iostream>#include<cstdio>#include<vector>#include<cstring>#include<cmath>#include<queue>#define maxn 10001+50using namespace std;int n;int c[maxn],dis[maxn];vector<int> g[maxn];vector<int> gg[maxn];queue<int> q;bool dfs(int u){    c[u]=-1;    int sz=g[u].size();    for(int i=0;i<sz;i++){        if(c[g[u][i]]<0) return false;        else if(!c[g[u][i]] && !dfs(g[u][i]))                return false;    }    c[u]=1;    return true;}bool toposort(){    for(int i=1;i<=n;i++)        c[i]=0;    for(int u=1;u<=n;u++) if(!c[u])        if(!dfs(u)) return false;    return true;}void bfs(int u){    while(!q.empty()) q.pop();    q.push(u);    while(!q.empty()){        int u=q.front();        q.pop();        int sz=gg[u].size();        for(int i=0;i<sz;i++){            int v=gg[u][i];            if(dis[u]<dis[v]) continue;            else{                dis[v]=dis[u]+1;                q.push(v);            }        }    }}int solve(){    int s=0;    for(int i=1;i<=n;i++)        dis[i]=888;    for(int i=1;i<=n;i++){        bfs(i);    }    for(int i=1;i<=n;i++)        s+=dis[i];    return s;}int main(){    int m,u,v;    while(~scanf("%d%d",&n,&m)){        for(int i=1;i<=n;i++) g[i].clear(),gg[i].clear();        for(int i=0;i<m;i++){            scanf("%d%d",&u,&v);            g[u].push_back(v);            gg[v].push_back(u);        }        if(toposort()){            printf("%d\n",solve());        }        else            printf("-1\n");    }    return 0;}