1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<cmath>
 6 using namespace std;
 7 int n,t,s,e,f[201][201][25],ans[2][201],num[1005],pos,logn;
 8 int main()
 9 {int i,d,u,v,p,j,k;
10     cin>>n>>t>>s>>e;
11     memset(f,127/3,sizeof(f));
12     memset(ans,127/2,sizeof(ans));
13     for (i=1;i<=t;i++)
14     {
15         scanf("%d%d%d",&d,&u,&v);
16         if (!num[u]) num[u]=++pos;
17         if (!num[v]) num[v]=++pos;
18         f[num[u]][num[v]][0]=f[num[v]][num[u]][0]=d;
19     }
20      logn=log2(n);
21       for (p=1;p<=logn;p++)
22       {
23             for (k=1;k<=pos;k++)
24             {
25                 for (i=1;i<=pos;i++)
26                 {
27                     for (j=1;j<=pos;j++)
28                     {
29                         f[i][j][p]=min(f[i][j][p],f[i][k][p-1]+f[k][j][p-1]);
30                     }
31                 }
32             }
33       }
34       t=0;p=0;
35       ans[0][num[s]]=0;
36         while (n)
37         {
38             if (n&1)
39             {
40                 t=!t;
41                  for (i=1;i<=pos;i++)
42                  {ans[t][i]=2e9;
43                     for (j=1;j<=pos;j++)
44                     {
45                         ans[t][i]=min(ans[t][i],ans[!t][j]+f[i][j][p]);
46                     }
47                  }
48             }
49             p++;
50             n/=2;
51         }
52     cout<<ans[t][num[e]];
53 }

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<cmath>
 6 using namespace std;
 7 int n,t,s,e,f[201][201],num[1005],pos;
 8 struct mat
 9 {
10     int s[101][101];
11     mat()
12     {int i,j;
13         for (i=1;i<=pos;i++)
14          for (j=1;j<=pos;j++)
15          s[i][j]=1e9;
16     }
17      mat operator*(const mat &x)
18      {int i,j,k;
19         mat ans;
20         for (k=1;k<=pos;k++)
21         {
22             for (i=1;i<=pos;i++)
23              {
24                 for (j=1;j<=pos;j++)
25                 {
26                     ans.s[i][j]=min(ans.s[i][j],s[i][k]+x.s[k][j]);
27                 }
28              }
29         }
30         return ans;
31      }
32 }S,T;
33 int main()
34 {int i,j,d,u,v;
35     cin>>n>>t>>s>>e;
36     for (i=1;i<=t;i++)
37     {
38         scanf("%d%d%d",&d,&u,&v);
39         if (!num[u]) num[u]=++pos;
40         if (!num[v]) num[v]=++pos;
41         f[num[u]][num[v]]=f[num[v]][num[u]]=d;
42     }
43     mat S,T;
44     for (i=1;i<=pos;i++)
45     for (j=1;j<=pos;j++)
46     if (f[i][j])
47      S.s[i][j]=T.s[i][j]=f[i][j];
48       n--;
49       while (n)
50       {
51             if (n&1)
52             {
53                 S=S*T;
54             }
55             T=T*T;
56             n>>=1;
57       }
58     cout<<S.s[num[s]][num[e]];
59 }