poj 3114 Countries in War（强连通缩点+最短路）

#include<cstdio>
#include<queue>
#include<cstring>
#include<iostream>
#include<algorithm>
#define debu
using  namespace std;
const int maxn=500+50;
const int maxm=250000+50;
const int INF=0x3f3f3f3f;
struct Node
{
int u,v,w;
Node(int u=0,int v=0,int w=0):u(u),v(v),w(w) {}
};
struct Edge
{
int to,w,next;
};
int s[100000+50];
Node e[maxm];
int vis[maxn],sc[maxn];
int v[maxn],dist[maxn];
int dfn[maxn],low[maxn];
int all,n,m,tot,top,cnt,q,tot2;
int head[maxm],head2[maxm];
Edge edge[maxm],edge2[maxm];
void addEdge(int u,int v,int w)
{
edge[tot].to=v,edge[tot].next=head[u];
edge[tot].w=w,head[u]=tot++;
}
void addEdge2(int u,int v,int w)
{
edge2[tot2].to=v,edge2[tot2].next=head2[u];
edge2[tot2].w=w,head2[u]=tot2++;
}
void Tarjan(int u)
{
all++,dfn[u]=low[u]=all;
top++,s[top]=u,vis[u]=1;
for(int i=head[u]; ~i; i=edge[i].next)
{
int nt=edge[i].to;
if(!dfn[nt])
{
Tarjan(nt);
low[u]=min(low[u],low[nt]);
}
else
{
if(vis[nt])
low[u]=min(low[u],dfn[nt]);
}
}
if(low[u]==dfn[u])
{
cnt++;
while(s[top+1]!=u)
{
sc[s[top]]=cnt;
vis[s[top]]=0;
top--;
}
}
}
void init()
{
all=tot=top=cnt=tot2=0;
memset(s,0,sizeof(s));
memset(sc,0,sizeof(sc));
memset(vis,0,sizeof(vis));
memset(dfn,0,sizeof(dfn));
memset(low,0,sizeof(low));
memset(head,-1,sizeof(head));
memset(head2,-1,sizeof(head2));
}
void SPFA(int s)
{
queue<int> q;
memset(v,0,sizeof(v));
for(int i=1; i<=n; i++) dist[i]=INF;
v[s]=1,q.push(s),dist[s]=0;
while(!q.empty())
{
int now=q.front();
q.pop(),v[now]=0;
for(int i=head2[now]; ~i; i=edge2[i].next)
{
int nt=edge2[i].to;
if(dist[nt]>dist[now]+edge2[i].w)
{
dist[nt]=dist[now]+edge2[i].w;
if(!v[nt])
{
v[nt]=1;
q.push(nt);
}
}
}
}
}
int main()
{
#ifdef debug
freopen("in.in","r",stdin);
#endif // debug
while(scanf("%d%d",&n,&m)!=EOF&&n)
{
init();
for(int i=0; i<m; i++)
{
int x,y,w;
scanf("%d%d%d",&x,&y,&w);
addEdge(x,y,w);
e[i]=Node(x,y,w);
}
for(int i=1; i<=n; i++)
if(!dfn[i]) Tarjan(i);
for(int i=0; i<m; i++)
{
int x=sc[e[i].u],y=sc[e[i].v];
if(x!=y) addEdge2(x,y,e[i].w);
}
scanf("%d",&q);
for(int i=0; i<q; i++)
{
int x,y,xx,yy;
scanf("%d%d",&x,&y);
xx=sc[x],yy=sc[y];
if(xx==yy) printf("0\n");
else
{
SPFA(xx);
if(dist[yy]>=INF) printf("Nao e possivel entregar a carta\n");
else printf("%d\n",dist[yy]);
}
}
printf("\n");
}
return 0;
}