Poj 1201 [not ac]

I haven't understood it for a long time.

First, give the code of a predecessor.

1 #include <iostream> 2 using namespace std; 3 struct Edge 4 { 5       int x,y,d; 6 }edge[50000+5]; 7 int n; 8 int d[50000+5]; 9 int main()10 {      11      while(scanf("%d",&n)!=EOF)12      {13             int Min=INT_MAX;14             int Max=INT_MIN;15             for(int i=0;i<n;++i)16             {17                   scanf("%d%d%d",&edge[i].x,&edge[i].y,&edge[i].d);18                   if(--edge[i].x<Min)Min=edge[i].x;19                   if(edge[i].y>Max)Max=edge[i].y;20             }21             int tmp=Max-Min+1;22             for(int i=Min;i<=Max;++i)23                   d[i]=INT_MIN;24             d[Min]=0;25             for(int i=0;i<tmp;++i)26             {27                   bool update=1;28                   for(int j=0;j<n;++j)29                   {30                         if(d[edge[j].x]!=INT_MIN&&d[edge[j].y]<d[edge[j].x]+edge[j].d) 31                         {32                               update=0;33                               d[edge[j].y]=d[edge[j].x]+edge[j].d;34                         }35                   }36                   for(int j=Min;j<Max;++j)37                   {38                         if(d[j]!=INT_MIN&&d[j]>d[j+1])39                         {40                               d[j+1]=d[j];41                               update=0;42                         }43                     }44                   for(int j=Max;j>Min;--j)45                   {46                         if(d[j]!=INT_MIN&&d[j]-1>d[j-1])47                         {48                               update=0;49                               d[j-1]=d[j]-1;50                         }51                   }52                   if(update)break;53             }54             printf("%d\n",d[Max]-d[Min]);55       }56       return 0;57 }

The analysis continues today, with some results. The Foundation is that the analysis is very slow. It's been a long time before you can understand it.