【wikioi1021】 玛丽卡

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
struct data{
int from,to,next,w;
}e[1000001];
int n,m,sum=0,head[1001],dis[1001],ans,father[1001],q[1000001];
bool del[1000001],inq[1001];
void insert(int u,int v,int w)
{
sum++;
e[sum].from=u;
e[sum].to=v;
e[sum].next=head[u];
e[sum].w=w;
head[u]=sum;
}
void spfa(int k)
{
memset(dis,127,sizeof(dis));
memset(inq,0,sizeof(inq));
memset(q,0,sizeof(q));
int t=0,w=1,now;
q[t]=1;inq[1]=1;dis[1]=0;
while(t<w){
int p=head[q[t]];
now=q[t];t++;
while(p){
if(!del[p]&&dis[now]+e[p].w<dis[e[p].to]){
dis[e[p].to]=dis[now]+e[p].w;
if(k==1)father[e[p].to]=p;
if(!inq[e[p].to]){
inq[e[p].to]=1;
q[w++]=e[p].to;
}
}
p=e[p].next;
}
inq[now]=0;
}
}
int main()
{
scanf("%d %d",&n,&m);
for(int i=1;i<=m;i++){
int a,b,v;
scanf("%d %d %d",&a,&b,&v);
insert(a,b,v);
insert(b,a,v);
}
spfa(1);
for(int i=n;i!=1;i=e[father[i]].from){
del[father[i]]=1;spfa(0);del[father[i]]=0;
ans=max(dis
,ans);
}
printf("%d",ans);
return 0;
}