[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;
}