Circle of Friends

感觉强连通缩点越写越顺手了（笑

若是能在练习的时候每次都写一遍不要粘贴那真是极好的

强连通缩点后bfs求最短路

勉强算一个dfs套bfs？（笑

----------------------------我是代码的昏割线----------------------

#include<bits/stdc++.h>
using namespace std;

const int maxn = 112345;

vector<int> edge[maxn];
vector<int> dcc[maxn];

int dfn[maxn],low[maxn],_cnt;
int bel[maxn];

stack<int> S;

void init(int n){
for(int i=0;i<=n;i++){
edge[i].clear();
dcc[i].clear();
}
memset(dfn,-1,sizeof(dfn));
memset(low,-1,sizeof(low));
memset(bel,-1,sizeof(bel));
_cnt = 0;
while(S.empty()==false){
S.pop();
}
}

#define iter vector<int>::iterator

void dfs(int st){
dfn[st] = low[st] = _cnt++;
S.push(st);
for(iter it = edge[st].begin();it!=edge[st].end();it++){
int x = *it;
if(dfn[x] == -1){
dfs(x);
low[st] = min(low[st],low[x]);
}
else if(bel[x] == -1){
low[st] = min(low[st],dfn[x]);
}
}
if(low[st] == dfn[st]){
while(S.top() != st){
bel[S.top()] = st;
S.pop();
}
bel[st] = st;
S.pop();
}
}

int dis[maxn];
queue<int> Q;

int bfs(int st,int ed){
while(Q.empty()==false)
Q.pop();
memset(dis,-1,sizeof(dis));
dis[st] = st;
Q.push(st);
while(Q.empty()==false){
st = Q.front();
Q.pop();
if(st == ed){
return dis[st];
}
for(iter it = dcc[st].begin();it!=dcc[st].end();it++){
if(dis[*it] == -1){
dis[*it] = dis[st] +1;
Q.push(*it);
}
}
}
return -1;
}

int main(){
int T;
scanf("%d",&T);
int n,m;
while(T-- && ~scanf("%d %d",&n,&m)){
init(n);
int x,y;
while(m--){
scanf("%d %d",&x,&y);
edge[x].push_back(y);
}
for(int i=0;i<n;i++){
if(dfn[i] == -1){
dfs(i);
}
}
for(int i=0;i<n;i++){
for(iter it = edge[i].begin();it!=edge[i].end();it++){
int st = bel[i];
int ed = bel[*it];
if(st != ed){
dcc[st].push_back(ed);
}
}
}
printf("%d\n",bfs(bel[0],bel[n-1]));
}
return 0;
}