[倍增Floyd] BZOJ 1706 [usaco2007 Nov]relays 奶牛接力跑

#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cstring>
using namespace std;

inline char nc()
{
static char buf[100000],*p1=buf,*p2=buf;
if (p1==p2) { p2=(p1=buf)+fread(buf,1,100000,stdin); if (p1==p2) return EOF; }
return *p1++;
}

inline void read(int &x)
{
char c=nc(),b=1;
for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;
for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;
}

const int N=205;

struct edge{
int u,v,w;
}G
;

int n,m,S,T;
int f

,h

,tmp

;
int sx
,icnt;

inline int Bin(int x){
return lower_bound(sx+1,sx+icnt+1,x)-sx;
}

int main()
{
freopen("t.in","r",stdin);
freopen("t.out","w",stdout);
read(n); read(m); read(S); read(T);
for (int i=1;i<=m;i++)
read(G[i].w),read(G[i].u),read(G[i].v),sx[++icnt]=G[i].u,sx[++icnt]=G[i].v;
sort(sx+1,sx+icnt+1);
icnt=unique(sx+1,sx+icnt+1)-sx-1;
for (int i=1;i<=m;i++)
G[i].u=Bin(G[i].u),G[i].v=Bin(G[i].v);
memset(f,0x3f,sizeof(f));
memset(h,0x3f,sizeof(h));
for (int i=1;i<=icnt;i++)
h[i][i]=0;
for (int i=1;i<=m;i++)
f[G[i].u][G[i].v]=f[G[i].v][G[i].u]=G[i].w;
for (int t=0;(1<<t)<=n;t++)
{
if (n&(1<<t))
{
memset(tmp,0x3f,sizeof(tmp));
for (int k=1;k<=icnt;k++)
for (int i=1;i<=icnt;i++)
for (int j=1;j<=icnt;j++)
tmp[i][j]=min(tmp[i][j],h[i][k]+f[k][j]);
memcpy(h,tmp,sizeof(tmp));
}
memset(tmp,0x3f,sizeof(tmp));
for (int k=1;k<=icnt;k++)
for (int i=1;i<=icnt;i++)
for (int j=1;j<=icnt;j++)
tmp[i][j]=min(tmp[i][j],f[i][k]+f[k][j]);
memcpy(f,tmp,sizeof(tmp));
}
printf("%d\n",h[Bin(S)][Bin(T)]);
return 0;
}