[bzoj1706] [usaco2007 Nov]relays 奶牛接力跑

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<cstdlib>
 6 #define ll long long
 7 #define ull unsigned long long
 8 #define d double
 9 using namespace std;
10 const int maxn=1023,inf=1002333333;
11 struct mat{int f[202][202];}f,c;
12 int id[1023];
13 int i,j,k,n,m,cnt,st,ed;
14 
15 int ra,fh;char rx;
16 inline int read(){
17     rx=getchar(),ra=0,fh=1;
18     while((rx<‘0‘||rx>‘9‘)&&rx!=‘-‘)rx=getchar();
19     if(rx==‘-‘)fh=-1,rx=getchar();
20     while(rx>=‘0‘&&rx<=‘9‘)ra*=10,ra+=rx-48,rx=getchar();return ra*fh;
21 }
22 inline int min(int a,int b){return a<b?a:b;}
23 inline mat run(mat &a,mat &b){
24     register int i,j,k;
25     for(i=1;i<=cnt;i++)for(j=1;j<=cnt;j++)
26         for(c.f[i][j]=inf,k=1;k<=cnt;k++)
27             c.f[i][j]=min(c.f[i][j],a.f[i][k]+b.f[k][j]);
28     return c;
29 }
30 int main(){
31     n=read(),m=read(),st=read(),ed=read();int x;
32     memset(f.f,60,sizeof(f.f));
33     for(i=1;i<=m;i++){
34         x=read(),j=read(),k=read();
35         if(!id[j])id[j]=++cnt;if(!id[k])id[k]=++cnt;
36         j=id[j],k=id[k];
37         f.f[j][k]=min(f.f[j][k],x),f.f[k][j]=min(f.f[k][j],x);
38     }
39     mat g=f;n--;
40     while(n){
41         if(n&1)g=run(g,f);
42         n>>=1;
43         if(n)f=run(f,f);
44     }
45     printf("%d\n",g.f[id[st]][id[ed]]);
46 }