Bzoj 1001 Wolf Catch rabbit Dual diagram +SPFA

The problem is to find the smallest cut of the graph, that is, the maximum flow. But because there are too many sides, the maximum flow algorithm is T, so the maximum flow algorithm cannot be used.

Because this is a plan, it is a special technique to find the minimum cut of a plane graph and then find the shortest path to the dual graph. Treat each face as a point the weight of the edge between the f*,f* is the weight of the edge that crosses the edge of the f* with the previous point F. (not clear, everyone can read other blogs, speak very well)

In this way, a dual graph g* is built, thus the g* of the dual graph corresponds to a cut of the original G. So the shortest way to find g* is equal to the minimum cut of G.

After encountering the plan to find the smallest cut it will be transformed into a dual graph to find the shortest way, so that time efficiency will be greatly improved.

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1#include <queue>2#include <cstdio>3#include <cstring>4#include <algorithm>5 using namespacestd;6 intpoint[2000103],next[6000103],v[6000103],c[6000103];7 intCnt=0, s,t,n,m,dist[2000103];8 BOOLvis[2000103];9queue<int>Q;Ten voidInsect (intXintYintz) One{Cnt++;next[cnt]=point[x];p oint[x]=cnt;v[cnt]=y;c[cnt]=Z;} A voidin1 () - { -     intI,j,num; the      for(j=1; j<m;++j) -     { -scanf"%d",&num); -Insect (j*2, t,num); +Insect (t,j*2, num); -     } +      for(i=2; i<n;++i) A       for(j=1; j<m;++j) at      { -scanf"%d",&num); -Insect ((I-1) * (M-1)*2+j*2, (I-1) * (M-1)*2+j*2-m*2+1, num); -Insect ((I-1) * (M-1)*2+j*2-m*2+1, (I-1) * (M-1)*2+j*2, num); -      } -      for(j=1; j<m;++j) in     { -scanf"%d",&num); toInsect (s, (n2)*2* (M-1) +j*2-1, num); +Insect ((n2)*2* (M-1) +j*2-1, s,num); -     } the } * voidin2 () $ {Panax Notoginseng     inti,j,num,xx; -      for(i=1; i<n;++i) the     { +scanf"%d", &num); xx= (I-1) * (M-1)*2+1; A insect (s,xx,num); the insect (xx,s,num); +          for(j=2; j<m;++j) -         { $scanf"%d", &num); xx+=2; $Insect (xx-1, xx,num); -Insect (xx,xx-1, num); -         } thescanf"%d",&num); -Insect (xx+1, t,num);WuyiInsect (t,xx+1, num); the     } - } Wu voidin3 () - { About     intI,j,num; $      for(i=1; i<n;++i) -       for(j=1; j<m;++j) -      { -scanf"%d",&num); AInsect ((I-1) * (M-1)*2+j*2-1, (I-1) * (M-1)*2+j*2, num); +Insect ((I-1) * (M-1)*2+j*2, (I-1) * (M-1)*2+j*2-1, num); the      } - } $ voidInit () the { thescanf"%d%d\n",&n,&m); thes=0; T= (n1) * (M-1)*2+1; the in1 (); - in2 (); in in3 (); the } the voidSPFA () About { the     intnum,mp; thedist[s]=0; the Q.push (s); +      while(!q.empty ()) -     { theNum=q.front (); Q.pop (); vis[num]=0;Bayimp=Point[num]; the          while(mp>0) the         { -             if(dist[v[mp]]>dist[num]+C[MP]) -             { thedist[v[mp]]=dist[num]+C[MP]; the                 if(vis[v[mp]]==0) the                 { thevis[v[mp]]=1; Q.push (V[mp]); -                 } the             } themp=NEXT[MP]; the         }94     } theprintf"%d\n", Dist[t]); the } the intMain ()98 { Aboutmemset (Dist,127,sizeof(Dist)); -memset (Point,0,sizeof(point));101Memset (Next,0,sizeof(next));102memset (Vis,0,sizeof(Vis));103memset (V,0,sizeof(v));104 init (); the SPFA ();106     return 0;107}

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• Floor plan Properties 1. (Euler's formula) if a connected plan has n points, M-and F-faces, then f=m-n+2 2. Each plot g has a planar graph with its dual g*n,g* each point corresponds to a polygon n in G

Bzoj 1001 Wolf Catch rabbit Dual diagram +SPFA