JZYZOJ1355 [usaco2007]奶牛赛跑 矩阵乘法 离散化

 1 #include<iostream>  
 2 #include<cstdio>  
 3 #include<cstring>  
 4 #include<algorithm>  
 5 #include<cmath>
 6 using namespace std;
 7 const int maxn=210;
 8 int n,m,s,t,siz;
 9 struct nod{int x,y,v;}aa[maxn];
10 struct mat{
11     int e[maxn][maxn];
12     mat(){memset(e,63,sizeof(e));}
13 };mat a;
14 int bb[maxn]={};
15 mat mul(mat x,mat y){
16     mat z;
17     for(int i=1;i<=siz;i++){
18         for(int j=1;j<=siz;j++){
19             for(int k=1;k<=siz;k++){
20                 z.e[i][j]=min(z.e[i][j],x.e[i][k]+y.e[k][j]);
21             }
22         }
23     }return z;
24 }
25 mat pow(mat x,int k){
26     mat z;
27     for(int i=1;i<=siz;i++){
28         z.e[i][i]=0;
29     }
30     while(k){
31         if(k&1)z=mul(z,x);
32         x=mul(x,x);
33         k/=2;
34     }
35     return z;
36 }
37 int main(){
38     scanf("%d%d%d%d",&n,&m,&s,&t);
39     for(int i=1;i<=m;i++){
40         scanf("%d%d%d",&aa[i].v,&aa[i].x,&aa[i].y);
41         bb[2*i-1]=aa[i].x;bb[2*i]=aa[i].y;
42     }sort(bb+1,bb+1+m*2);
43     siz=unique(bb+1,bb+1+m*2)-bb-1;
44     s=lower_bound(bb+1,bb+1+siz,s)-bb;
45     t=lower_bound(bb+1,bb+1+siz,t)-bb;
46     for(int i=1;i<=m;i++){
47         aa[i].x=lower_bound(bb+1,bb+1+siz,aa[i].x)-bb;
48         aa[i].y=lower_bound(bb+1,bb+1+siz,aa[i].y)-bb;
49         a.e[aa[i].x][aa[i].y]=aa[i].v;
50         a.e[aa[i].y][aa[i].x]=aa[i].v;
51     }
52     mat z=pow(a,n);
53     printf("%d\n",z.e[s][t]);
54     return 0;
55 }