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| #include<bits/stdc++.h>
#define RG register
#define file(x) freopen(#x".in", "r", stdin);freopen(#x".out", "w", stdout);
#define clear(x, y) memset(x, y, sizeof(x));
using namespace std;
template<typename T = int>
inline T read()
{
T data=0, w=1;
char ch=getchar();
while(ch!='-'&&(ch<'0'||ch>'9')) ch=getchar();
if(ch=='-') w=-1, ch=getchar();
while(ch>='0'&&ch<='9') data=(data<<3)+(data<<1)+(ch^48), ch=getchar();
return data*w;
}
const int N(210);
typedef long long ll;
int k, t, s, e, cnt, pos[2010];
class Matrix
{
private:
ll a[N][N];
public:
Matrix() { clear(a, 0x3f); }
ll *operator [] (int index) { return a[index]; }
Matrix operator * (Matrix &b)
{
Matrix c;
for(RG int k=1;k<=cnt;k++)
for(RG int i=1;i<=cnt;i++)
for(RG int j=1;j<=cnt;j++)
c[i][j]=min(c[i][j], a[i][k]+b[k][j]);
return c;
}
}G, A;
ll x, y, z;
int main()
{
k=read(); t=read(); s=read(); e=read();
for(RG int i=1;i<=t;i++)
{
z=read(); x=read(); y=read();
if(!pos[x]) pos[x]=++cnt;
if(!pos[y]) pos[y]=++cnt;
G[pos[x]][pos[y]]=G[pos[y]][pos[x]]=min(G[pos[x]][pos[y]], z);
}
for(RG int i=1;i<=cnt;i++) A[i][i]=0;
while(k)
{
if(k&1) A=A*G;
G=G*G;
k>>=1;
}
printf("%lld\n", A[pos[s]][pos[e]]);
return 0;
}
|