[USACO07NOV]Cow Relays

离散化+倍增优化Floyed

#include"cstdio"
#include"cstring"
#include"iostream"
#include"algorithm"
using namespace std;

const int MAXN=205;
const int MAXM=1005;

int n,T,S,E,cnt,mx,mi=MAXM;
int st[MAXM],s[MAXM];
int x[MAXN],y[MAXN],ln[MAXN];
struct Matrix{
	int v[MAXN][MAXN];
	int x,y;
	
	void clear(){memset(v,0,sizeof(v));x=y=0;return;}
	void Mmul(Matrix a,Matrix b)
	{
		memset(v,0x3f,sizeof(v));
		x=a.x,y=b.y;
		int c=a.y;
		for(int k=1;k<=c;++k){
			for(int i=1;i<=x;++i){
				for(int j=1;j<=y;++j){
					v[i][j]=min(v[i][j],a.v[i][k]+b.v[k][j]);
				}
			}
		}return;
	}
	
	Matrix Mpw(Matrix a,int b)
	{
		Matrix x=a;
		while(b){
			if(b&1) x.Mmul(x,a);
			b>>=1;a.Mmul(a,a);
		}return x;
	}
	
	void write()
	{
		for(int i=1;i<=x;++i){
			for(int j=1;j<=y;++j){
				printf("%d ",v[i][j]);
			}puts("");
		}puts("");
		return;
	}
}F;

int main()
{
	scanf("%d%d%d%d",&n,&T,&S,&E);
	for(int i=1;i<=T;++i){
		scanf("%d%d%d",&ln[i],&x[i],&y[i]);
		st[x[i]]=st[y[i]]=1;
		mi=min(mi,min(x[i],y[i]));
		mx=max(mx,max(x[i],y[i]));
	}for(int i=mi;i<=mx;++i) if(st[i]) s[i]=++s[0];
	S=s[S],E=s[E];
	memset(F.v,0x3f,sizeof(F.v));
	F.x=F.y=s[0];
	for(int i=1;i<=T;++i) F.v[s[x[i]]][s[y[i]]]=F.v[s[y[i]]][s[x[i]]]=ln[i];
	F=F.Mpw(F,n-1);
	printf("%d\n",F.v[S][E]);
	return 0;
}