【luogu P3063 [USACO12DEC]牛奶的路由Milk Routing】 题解

题目链接：https://www.luogu.org/problemnew/show/P3063#sub

我很好奇这道题为什么没被收入SPFA好题

#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
using namespace std;
const int maxn = 20001;
const int inf = 0x7fffffff-1;
int n, m, s, f, x, k, ans = inf, dis[maxn], c[maxn];
bool vis[maxn];
struct edge{
    int to, next, len, from, l;
}e[maxn];
int head[maxn], cnt;
void add(int u, int v, int w, int l)
{
    e[++cnt].from = u;
    e[cnt].to = v;
    e[cnt].len = w;
    e[cnt].l = l;
    e[cnt].next = head[u];
    head[u] = cnt;
}
int SPFA(int k)
{
    queue<int> q;
    memset(vis,0,sizeof(vis));
    memset(dis,127,sizeof(dis));
    dis[s] = 0;
       q.push(s);
    vis[s] = 1;
    while(!q.empty())
    {
        int now = q.front();
        q.pop();
        vis[now] = 0;
        for(int i = head[now]; i ; i = e[i].next)
        {
            if(dis[e[i].to] > dis[now]+e[i].len && e[i].l >= k)
            {
                dis[e[i].to] = dis[now]+e[i].len;
                if(!vis[e[i].to])
                {
                    vis[e[i].to] = 1;
                    q.push(e[i].to);
                }
            }
        }
    }
}
int main()
{
    scanf("%d%d%d",&n,&m,&x);
    for(int i = 1; i <= m; i++)
    {
        int u,v,w,l;
        scanf("%d%d%d%d",&u,&v,&w,&l);
        add(u,v,w,l);
        add(v,u,w,l);
        c[i] = l;
    }
    sort(c+1,c+m+1);
    s = 1, f = n;
    for(int i = 1; i <= m; i++)
    {
        SPFA(c[i]);
        ans = min(ans, dis[f]+x/c[i]);
    }
    printf("%d",ans);
}