576D Flights for Regular Customers

分析

https://www.cnblogs.com/onioncyc/p/8037056.html

写的好像有点问题

但是大致就是这个意思

代码很好理解

代码

#include<bits/stdc++.h>
using namespace std;
#define bt bitset<160>
const int inf = 0x3f3f3f3f;
int n,m,g[][];
bt ans[],a[],c[];
struct node {
    int x,y,z;
};
node d[];
inline bool cmp(const node x,const node y){return x.z<y.z;}
inline void mul(bt a[],bt b[]){
    int i,j,k;
    for(i=;i<=n;i++)c[i].reset();
    for(k=;k<=n;k++)
      for(i=;i<=n;i++)
        if(a[i][k])c[i]|=b[k];
    for(i=;i<=n;i++)a[i]=c[i];
}
int main(){
    int i,j,k;
    scanf("%d%d",&n,&m);
    for(i=;i<=m;i++)scanf("%d%d%d",&d[i].x,&d[i].y,&d[i].z);
    sort(d+,d+m+,cmp);
    for(i=;i<=n;i++)ans[i].reset();
    for(i=;i<=n;i++)ans[i][i]=;
    int Ans=inf;
    for(int _=;_<=m;_++){
      for(i=;i<=n;i++)a[i].reset();
      for(i=;i<_;i++)a[d[i].x][d[i].y]=;
      k=d[_].z-d[_-].z;
      while(k){
          if(k&)mul(ans,a);
          mul(a,a);
          k>>=;
      }
      memset(g,0x3f,sizeof(g));
      for(i=;i<=n;i++)g[i][i]=;
      for(i=;i<=_;i++)g[d[i].x][d[i].y]=;
      for(k=;k<=n;k++)
        for(i=;i<=n;i++)
          for(j=;j<=n;j++)
            g[i][j]=min(g[i][j],g[i][k]+g[k][j]);
      for(i=;i<=n;i++)if(ans[][i])Ans=min(Ans,d[_].z+g[i][n]);
    }
    if(Ans==inf)puts("Impossible");else printf("%d\n",Ans);
    return ;
}