51nod 1076 2条不相交的路径

Posted 2020-09-27 早知如此绊人心，何如当初莫相识。

思路：强连通，将他变成有向图，并且不能返回父节点

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int maxn=30000;
 4 
 5 struct node{
 6     int v,next;
 7 }edg[50004*3];
 8 int head[maxn],tot=0;
 9 void add(int u,int v){
10     edg[tot].v=v;edg[tot].next=head[u];head[u]=tot++;
11 }
12 int dfn[maxn],low[maxn],belong[maxn];
13 bool instack[maxn];
14 int Stack[maxn],index,top,bcnt;
15 set<int >s[maxn];
16 void dfs(int u,int fa)
17 {
18     dfn[u]=low[u]=++index;
19     Stack[++top]=u;
20     instack[u]=true;
21     for(int i=head[u];i!=-1;i=edg[i].next)
22     {
23         int v=edg[i].v;
24         if(!dfn[v]){
25             dfs(v,u);
26             low[u]=min(low[u],low[v]);
27         }else if(instack[v]&&v!=fa) low[u]=min(low[u],dfn[v]);
28     }
29     int v;
30     if(dfn[u]==low[u]){
31         bcnt++;
32         do{
33             v=Stack[top--];
34             instack[v]=false;
35             belong[v]=bcnt;
36           //  s[bcnt].insert(v);
37         }while(u!=v);
38     }
39 }
40 int n,m;
41 void Tarjan()
42 {
43     memset(dfn,0,sizeof(dfn));
44     bcnt = top = index = 0;
45     for(int i=1;i<=n;i++)
46         if(!dfn[i])
47             dfs(i,-1);
48 }
49 
50 int main(){
51     int x,y;
52    memset(head,-1,sizeof(head));
53    scanf("%d%d",&n,&m);
54    for(int i=1;i<=m;i++){
55         scanf("%d%d",&x,&y);
56         add(x,y);add(y,x);
57    }
58    Tarjan();
59    //for(int i=1;i<=n;i++) cout<<belong[i]<<endl;
60    int q;
61    scanf("%d",&q);
62    while(q--){
63         scanf("%d%d",&x,&y);
64      //   cout<<belong[x]<<" "<<belong[y]<<" "<<s[belong[x]].size()<<endl;
65         if(belong[x]==belong[y]){
66             cout<<"Yes"<<endl;
67         }
68         else cout<<"No"<<endl;
69    }
70    return 0;
71 }