codevs——2645 Spore

#include<queue>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#define N 20010
#define maxn 999999
using namespace std;
bool vist,vis[N];
int n,m,x,y,z,w,tot;
int in[N],dis[N],head[N];
int read()
{
    int x=0,f=1; char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1; ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘; ch=getchar();}
    return x*f;
}
struct Edge
{
    int to,from,dis,next;
}edge[N];
int add(int x,int y,int z)
{
    tot++;
    edge[tot].to=y;
    edge[tot].dis=z;
    edge[tot].next=head[x];
    head[x]=tot;
}
void begin()
{
    tot=vist=0;
    memset(in,0,sizeof(in));
    memset(dis,0,sizeof(dis));
    memset(vis,0,sizeof(vis));
    memset(head,0,sizeof(head));
}
int spfa(int s)
{
    queue<int>q; bool vis[N];
    for(int i=1;i<=n;i++) vis[i]=false,dis[i]=maxn;
    q.push(s),vis[s]=true,dis[s]=0;
    while(!q.empty())
    {
        int x=q.front();q.pop();
        for(int i=head[x];i;i=edge[i].next)
        {
            int t=edge[i].to;
            if(dis[t]>dis[x]+edge[i].dis)
            {
                dis[t]=dis[x]+edge[i].dis;
                if(!vis[t])
                {
                    in[t]++;
                    vis[t]=true;
                    q.push(t);
                    if(in[t]>n) return true;
                }
            }
        }
        vis[x]=false;
    }
    return false;
}
int main()
{
    while(1)
    {
        n=read(),m=read();
        begin();
        if(n==0&&m==0) break;
        for(int i=1;i<=m;i++)
        {
            x=read(),y=read(),z=read(),w=read();
            add(x,y,z),add(y,x,w);
        }
        vist=spfa(1);
        if(vist||dis[n]==maxn) printf("No such path\n");
        else  printf("%d\n",dis[n]);
    }
    return 0;
}