UVa10917 Walk Through the Forest

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<queue>
using namespace std;
const int maxn=1005,maxm=(maxn-1)*(maxn-2);
const int INF=1e9;
int a[maxn],d[maxn],h[maxn],cnt,n,m;
bool vis[maxn];
struct Edge{
int t,d,nxt;
Edge(int a=0,int b=0,int c=0):t(a),d(b),nxt(c){}
}edges[maxm*2];
struct heap{
int d,v;
heap(int a=0,int b=0):d(a),v(b){}
bool operator<(const heap&a)const{
return d>a.d;
}
};
void addedge(int from,int to,int dist){
edges[++cnt]=Edge(to,dist,h[from]);
h[from]=cnt;
edges[++cnt]=Edge(from,dist,h[to]);
h[to]=cnt;
}
int dfs(int u){
if(a[u]>-1) return a[u];
a[u]=0;
for(int i=h[u];i;i=edges[i].nxt){
int v=edges[i].t;
if(d[u]<d[v]) a[u]+=dfs(v);
}
return a[u];
}
int main(){
while(scanf("%d",&n)==1&&n){
scanf("%d",&m);
cnt=0;
memset(h,0,sizeof(h));
for(int i=0;i<m;i++){
int a,b,c;
scanf("%d%d%d",&a,&b,&c);
addedge(a,b,c);
}
priority_queue<heap> q;
q.push(heap(0,2));
for(int i=1;i<=n;i++) d[i]=INF;
d[2]=0;
memset(vis,0,sizeof(vis));
while(!q.empty()){
heap x=q.top();q.pop();
int u=x.v;
if(vis[u]) continue;
vis[u]=1;
for(int i=h[u];i;i=edges[i].nxt){
int v=edges[i].t;
if(d[u]+edges[i].d<d[v]){
d[v]=d[u]+edges[i].d;
q.push(heap(d[v],v));
}
}
}
memset(a,-1,sizeof(a));
memset(vis,0,sizeof(vis));
a[1]=1;
printf("%d\n",dfs(2));
}
return 0;
}