【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

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <queue>
 4 #include <algorithm>
 5 using namespace std;
 6 const int maxn = 20001;
 7 const int inf = 0x7fffffff-1;
 8 int n, m, s, f, x, k, ans = inf, dis[maxn], c[maxn];
 9 bool vis[maxn];
10 struct edge{
11     int to, next, len, from, l;
12 }e[maxn];
13 int head[maxn], cnt;
14 void add(int u, int v, int w, int l)
15 {
16     e[++cnt].from = u;
17     e[cnt].to = v;
18     e[cnt].len = w;
19     e[cnt].l = l;
20     e[cnt].next = head[u];
21     head[u] = cnt;
22 }
23 int SPFA(int k)
24 {
25     queue<int> q;
26     memset(vis,0,sizeof(vis));
27     memset(dis,127,sizeof(dis));
28     dis[s] = 0;
29        q.push(s);
30     vis[s] = 1;
31     while(!q.empty())
32     {
33         int now = q.front();
34         q.pop();
35         vis[now] = 0;
36         for(int i = head[now]; i ; i = e[i].next)
37         {
38             if(dis[e[i].to] > dis[now]+e[i].len && e[i].l >= k)
39             {
40                 dis[e[i].to] = dis[now]+e[i].len;
41                 if(!vis[e[i].to])
42                 {
43                     vis[e[i].to] = 1;
44                     q.push(e[i].to);
45                 }
46             }
47         }
48     }
49 }
50 int main()
51 {
52     scanf("%d%d%d",&n,&m,&x);
53     for(int i = 1; i <= m; i++)
54     {
55         int u,v,w,l;
56         scanf("%d%d%d%d",&u,&v,&w,&l);
57         add(u,v,w,l);
58         add(v,u,w,l);
59         c[i] = l;
60     }
61     sort(c+1,c+m+1);
62     s = 1, f = n;
63     for(int i = 1; i <= m; i++)
64     {
65         SPFA(c[i]);
66         ans = min(ans, dis[f]+x/c[i]);
67     }
68     printf("%d",ans);
69 }