51Nod--1076 2条不相交的路径（强连通分量）

 

电波

#include<bits/stdc++.h>
using namespace std;
#define LL long long
#define maxn 30000
vector<int>q[maxn];
int dfn[maxn],low[maxn],st[maxn],vis[maxn],top;
int num[maxn],i;
void dfs(int u,int deep,int fa){
   dfn[u]=deep;
   low[u]=deep;
   st[++top]=u;
   vis[u]=1;
   for(int j=0;j<q[u].size();j++){
       int v=q[u][j];
       if(v==fa) continue;
       if(!dfn[v]){
          dfs(v,deep+1,u);
          low[u]=min(low[u],low[v]);
       }else if(vis[v]){
          low[u]=min(low[u],low[v]);
       }
   }
   if(low[u]==dfn[u]){
       num[u]=++i;
       vis[u]=0;
       while(st[top]!=u){
          num[st[top]]=i;
          vis[st[top]]=0,top--;
       }
       top--;
   }
}
int main(){
     int n,m;
     cin>>n>>m;
     memset(vis,0,sizeof(vis));
     memset(dfn,0,sizeof(dfn));
     for(int j=0;j<m;j++){
        int u,v;
        scanf("%d%d",&u,&v);
        q[u].push_back(v);
        q[v].push_back(u);
     }
     top=0,i=0;
     for(int j=1;j<=n;j++){
        if(!dfn[j]){
           dfs(j,1,j);
        }
     }
     int z;
     cin>>z;
     for(int j=0;j<z;j++){
        int u,v;
        scanf("%d%d",&u,&v);
        if(num[u]==num[v]){
           printf("Yes
");
        }else{
           printf("No
");
        }
     }
  return 0;
}