Educational Codeforces Round 10 E. Pursuit For Artifacts 强连通缩点+bfs

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
using namespace std;
const int MAXN=4e5+100;
const int MAXM=2*MAXN;

struct Edge
{
int to,next,cut,val;
} edge[MAXM];

int head[MAXN],tot,low[MAXN],dfn[MAXN],Stack[MAXN],Belong[MAXN];//Belong数组是连通块的序号
int index,top,st,ed;
int block;
int instack[MAXN],has[MAXN],vis[MAXN];
int bridge;
vector<Edge>G[MAXN];
queue<int>q;
void addedge(int u,int v,int val)
{
edge[tot].to=v;
edge[tot].next=head[u];
edge[tot].cut=0;
edge[tot].val=val;
head[u]=tot++;
}

void Tarjan(int u,int pre)
{
int v;
low[u]=dfn[u]=++index;
Stack[top++]=u;
instack[u]=1;
for(int i=head[u]; i!=-1; i=edge[i].next)
{
v=edge[i].to;
if(v==pre) continue;
if(!dfn[v])
{
Tarjan(v,u);
if(low[u]>low[v]) low[u]=low[v];
if(low[v]>dfn[u])
{
bridge++;
edge[i].cut=1;
edge[i^1].cut=1;
}
}
else if(instack[v]&&low[u]>dfn[v])
low[u]=dfn[v];
}
if(low[u]==dfn[u])
{
block++;
do
{
v=Stack[--top];
instack[v]=0;
Belong[v]=block;
}
while(v!=u);
}
}

void init()
{
tot=0;
memset(head,-1,sizeof(head));
}

int solve(int n)
{
memset(dfn,0,sizeof(dfn));
memset(instack,0,sizeof(instack));
memset(Belong,0,sizeof(Belong));
index=top=block=0;
Tarjan(1,0);
for(int i=1;i<=n;i++)
{
if(Belong[i]==0)
{
block++;
Belong[i]=block;
}
}
for(int i=1; i<=block; i++)
{
has[i]=0;
G[i].clear();
}
int u,v,now;
Edge e;

for(int i=1; i<=n; i++)
{
for(int j=head[i]; j!=-1; j=edge[j].next)
{
if(edge[j].cut)
{
u=Belong[i];
v=Belong[edge[j].to];
e.to=v;
e.val=edge[j].val;
G[u].push_back(e);
}
else if(edge[j].val==1)
has[Belong[i]]=1;
}
}
u=Belong[st];
v=Belong[ed];
memset(vis,0,sizeof(vis));
if(u==v) return has[v];
else
{
q.push(u);
vis[u]=1;
while(!q.empty())
{
u=q.front();
q.pop();
for(int i=0;i<G[u].size();i++)
{
now=G[u][i].to;
if(vis[now]) continue;
else vis[now]=1;
if(has[u]==1||has[now]==1||G[u][i].val==1) has[now]=1;
else has[now]=0;
if(now==v) return has[now];
q.push(now);
}
}
return 0;
}
}

int main()
{
int n,m;
int u,v,w,k;
while(~scanf("%d%d",&n,&m))
{
init();
for(k=1; k<=m; k++)
{
scanf("%d%d%d",&u,&v,&w);
addedge(u,v,w);
addedge(v,u,w);
}
scanf("%d%d",&st,&ed);
if(solve(n)==1) puts("YES");
else puts("NO");
}
return 0;
}