【SDUTOJ 3262】省赛L 强连通缩点

SDUT 3262 Circle of Friends
模板题 强连通缩点+DFS

#include 
#include 
#include 
#include 
#include 
#include 

using namespace std;

typedef struct Edge
{
    int v,next;
}Edge;

stack <int> s;
int vis[111111];
int dfn[111111],low[111111];
int pt[111111];
int step[111111];
Edge eg[111111],eg2[111111];
int head[111111],head2[111111];
int n,m;
int point,tim,tp;


void Init()
{
    memset(step,-1,sizeof(step));
    memset(pt,0,sizeof(pt));
    memset(dfn,0,sizeof(dfn));
    memset(vis,0,sizeof(vis));
    memset(head,-1,sizeof(head));
    memset(head2,-1,sizeof(head2));
    tp = tim = point = 0;
}

void Tarjan(int u)
{
    dfn[u] = low[u] = ++tim;
    s.push(u);
    vis[u] = -1;
    int v,i;
    for(i = head[u]; i != -1; i = eg[i].next)
    {

        v = eg[i].v;
        if(!vis[v])
        {
            Tarjan(v);
            low[u] = min(low[v],low[u]);
        }
        else if(vis[v] == -1)
        {
            low[u] = min(low[u],dfn[v]);
        }
    }

    if(dfn[u] == low[u])
    {
        ++point;
        while(!s.empty())
        {
            v = s.top();
            pt[v] = point;
            vis[v] = 1;
            s.pop();
            if(dfn[v] == low[u]) break;
        }
    }
}

void GetMap()
{
    int i,j,u,v;
    for(i = 0; i < n; ++i)
    {
        u = pt[i];
        for(j = head[i]; j != -1; j = eg[j].next)
        {
            v = eg[j].v;
            if(pt[v] == u) continue;
            //cout<"<"<
            eg2[tp].v = pt[v];
            eg2[tp].next = head2[u];
            head2[u] = tp++;
        }
    }
}

void Bfs()
{
    queue <int> q;
    q.push(pt[0]);
    memset(vis,0,sizeof(vis));
    step[pt[0]] = 0;
    vis[pt[0]] = 1;
    int i,u;
    while(!q.empty())
    {
        u = q.front();
        q.pop();
        for(i = head2[u]; i != -1; i = eg2[i].next)
        {
            int v = eg2[i].v;
            if(!vis[v])
            {
                //cout<"<
                step[v] = step[u]+1;
                q.push(v);
                vis[v] = 1;
            }
            if(v == pt[n-1]) return;
        }
    }
}

int main()
{
    int t,i,u;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d %d",&n,&m);
        Init();
        for(i = 0; i < m; ++i)
        {
            scanf("%d %d",&u,&eg[i].v);
            eg[i].next = head[u];
            head[u] = i;
        }
        Tarjan(0);
        GetMap();
        Bfs();
        printf("%d\n",step[pt[n-1]]);
    }
    return 0;
}