Walk Through the Forest UVA - 10917 DAG上的图

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#include<string>
#include<cstring>
#include<iomanip>
#include<iostream>
#include<stack>
#include<cmath>
#include<map>
#include<vector>
#define ll long long
#define inf 0x3f3f3f3f
#define INF 1e9
#define bug1 cout<<"bug1"<<endl;
#define bug2 cout<<"bug2"<<endl;
#define bug3 cout<<"bug3"<<endl;
using namespace std;
#define sf scanf
#define pf printf
#define mem(a,b) memset(a,b,sizeof(a));
const int maxn=1005;
int n,m;
int vis[maxn];
int d[maxn];
int dp[maxn];
int head[maxn];
struct Edge{
int v,c,nxt;
}edge[maxn*maxn];
int tol;
void addedge(int u,int v,int c){
edge[tol].v=v;edge[tol].c=c;
edge[tol].nxt=head[u];
head[u]=tol++;
}
void spfa(int s){
queue<int>q;
mem(d,inf);
mem(vis,0);
q.push(s);
d[s]=0;
vis[s]=1;
while(!q.empty()){
int u=q.front();q.pop();
vis[u]=0;
for(int i=head[u];~i;i=edge[i].nxt){
int v=edge[i].v;
if(d[v]>d[u]+edge[i].c){
d[v]=d[u]+edge[i].c;
if(!vis[v]){
vis[v]=1;q.push(v);
}
}
}
}
}
vector<int>sons[maxn];
void dfs1(int u){
vis[u]=1;
if(u==2)return;
for(int i=head[u];~i;i=edge[i].nxt){
int v=edge[i].v;
if(d[v]<d[u]){
sons[u].push_back(v);
if(!vis[v])dfs1(v);
}
}
}
int dfs(int u){
if(u==2)return dp[u]=1;
if(dp[u]!=-1)return dp[u];
dp[u]=0;
for(int i=0;i<sons[u].size();++i){
dp[u]+=dfs(sons[u][i]);
}
return dp[u];
}
int main(){
while(~sf("%d%d",&n,&m)&&n){
tol=0;mem(head,-1);
for(int i=1;i<=m;++i){
int u,v,c;
sf("%d%d%d",&u,&v,&c);
addedge(u,v,c);
addedge(v,u,c);
}
spfa(2);
mem(vis,0);
for(int i=1;i<=n;++i){
sons[i].clear();
}
dfs1(1);
mem(dp,-1);
dfs(1);
pf("%d\n",dp[1]);
}
}