tarjan求强连通分量

http://poj.org/problem?id=3180

//#include<bits/stdc++.h>
#include<iostream>
#include<cstdio>
#include<iomanip>
#include<cmath>
#include<algorithm>
#include<vector>
#include<cstring>
#include<queue>
#include<map>
#include<string>
#include<stack>
#define fi first
#define se second
#define INF 0x3f3f3f3f
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define pqueue priority_queue
#define NEW(a,b) memset(a,b,sizeof(a))
#define lowbit(x) ((x)&(-x))
const double pi=4.0*atan(1.0);
const int maxn=1e5+8;
typedef long long LL;
typedef unsigned long long ULL;
const LL mod=1e9+7;
const ULL base=1e7+7;
using namespace std;
struct node{
    int to,nxt;
}g[maxn*2];
int head[maxn];
int cnt=0;
void add(int u,int v){
    g[cnt].to=v;
    g[cnt].nxt=head[u];
    head[u]=cnt++;
}
int deep=0;
int dfn[maxn],low[maxn];
bool vis[maxn];
int Stack[maxn];
int tail=0;
int ans=0;
void tarjan(int u){
    dfn[u]=++deep;
    low[u]=deep;
    Stack[++tail]=u;
    vis[u]=1;
    int t=head[u];
    int r=0;
    while(t!=-1){
        if(!dfn[g[t].to]){
            tarjan(g[t].to);
            low[u]=min(low[u],low[g[t].to]);
        }
        else{
            if(vis[g[t].to]){
                low[u]=min(low[u],low[g[t].to]);
            }
        }
        t=g[t].nxt;
    }
    if(dfn[u]==low[u]){
        while(Stack[tail]!=u){
            vis[Stack[tail]]=0;
            tail--;
            r=1;
        }
        vis[Stack[tail]]=0;
        tail--;
    }
    ans+=r;
}
int main(){
    memset(head,-1,sizeof(head));
    int n,m,x,y;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++){
        scanf("%d%d",&x,&y);
        add(x,y);
    }
    for(int i=1;i<=n;i++){
        if(!dfn[i]){
            tarjan(i);
        }
    }
    cout<<ans<<endl;
}

无向图缩点

http://codeforces.com/group/w1oiqifZbS/contest/652/problem/E

#include<bits/stdc++.h>
#define fi first
#define se second
#define INF 0x3f3f3f3f
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define pqueue priority_queue
#define NEW(a,b) memset(a,b,sizeof(a))
#define lowbit(x) ((x)&(-x))
const double pi=4.0*atan(1.0);
const int maxn=3e5+8;
typedef long long LL;
typedef unsigned long long ULL;
const LL mod=1e9+7;
const ULL base=1e7+7;
using namespace std;
struct node{
    int to,nxt;
    bool val;
}g[maxn*2],gg[maxn*2];
int head[maxn],head2[maxn];
int cnt=0;
void add(int u,int v,bool val){
    g[cnt].to=v;
    g[cnt].nxt=head[u];
    g[cnt].val=val;
    head[u]=cnt++;
}
int deep=0;
int dfn[maxn],low[maxn];
bool vis[maxn];
bool used[maxn];
int Stack[maxn];
bool a[maxn];
int color[maxn];
int tot=0;
int tail=0;
int n,m;
void tarjan(int u,int fa){
    dfn[u]=++deep;
    low[u]=deep;
    Stack[++tail]=u;
    vis[u]=1;
    int t=head[u];
    while(t!=-1){
        if(g[t].to==fa){
            t=g[t].nxt;
            continue;
        }
        if(!dfn[g[t].to]){
            tarjan(g[t].to,u);
            low[u]=min(low[u],low[g[t].to]);
        }
        else{
            if(vis[g[t].to]){
                low[u]=min(low[u],low[g[t].to]);
            }
        }
        t=g[t].nxt;
    }
    if(dfn[u]==low[u]){
        tot++;
        while(Stack[tail]!=u){
            vis[Stack[tail]]=0;
            color[Stack[tail]]=tot;
            tail--;
        }
        vis[Stack[tail]]=0;
        color[Stack[tail]]=tot;
        tail--;
    }
}
void add2(int u,int v,int val){
    gg[cnt].to=v;
    gg[cnt].nxt=head2[u];
    gg[cnt].val=val;
    head2[u]=cnt++;
}
void suodian(){
    for(int i=1;i<=n;i++){
        int t=head[i];
        while(t!=-1){
            if(color[i]==color[g[t].to]){
                a[color[i]]+=g[t].val;
            }
            else if(g[t].to>i){
                //cout<<i<<' '<<g[t].to<<endl;
                add2(color[i],color[g[t].to],g[t].val);
                add2(color[g[t].to],color[i],g[t].val);
            }
            t=g[t].nxt;
        }
    }
}
bool ans=0;
void dfs2(int u,int fa,int aim,bool re){
    //cout<<u<<endl;
    if(u==aim){
        ans+=re;
        return ;
    }
    int t=head2[u];
    while(t!=-1){
        if(gg[t].to!=fa){
            dfs2(gg[t].to,u,aim,re+gg[t].val+a[gg[t].to]);
        }
        t=gg[t].nxt;
    }
}
int main(){
    memset(head,-1,sizeof(head));
    memset(head2,-1,sizeof(head2));
    int x,y,val;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++){
        scanf("%d%d%d",&x,&y,&val);
        add(x,y,(bool)val);
        add(y,x,(bool)val);
    }
    int s,t;
    scanf("%d%d",&s,&t);
    for(int i=1;i<=n;i++){
        if(!dfn[i]){
            tarjan(i,0);
        }
    }
    cnt=0;
    suodian();
    dfs2(color[s],0,color[t],a[color[s]]);
    if(ans){
        cout<<"YES"<<endl;
    }
    else{
        cout<<"NO"<<endl;
    }
}