COGS746. [Network Flow 24 questions] Knight Coexistence

Knight Coexistence Issues
«Problem Description:
On a n*n chess board, a horse (Knight) can attack a checkerboard. Board

Some squares are disabled and the knight is not allowed to enter.

«Programming Tasks:
For a given n*n checkered chess board and barrier markers, calculate the maximum number of rides on the board that can be placed
They are not attacking each other.
«Data Entry:
The input data is given by the file knight.in. The first line has 2 positive integers n and M (1<=n<=200, 0<=m<=n*n) <n2),< span= "" >
Indicates the size and number of obstacles for the board, respectively. The next M-line gives the position of the barrier. 2 positive integers per line, indicating a barrier
The grid coordinates of the obstruction.
«Result Output:
Outputs the calculated coexistence Knight number to file Knight.out.
Example output file for input file sample
Knight.in
3 2
1 1

3 3

Knight.out

5

The maximum independent set of the binary graph is converted to the maximum matching of two graph, thus solving with maximum flow.

1#include <iostream>2#include <cstdio>3#include <algorithm>4#include <cstring>5#include <queue>6#include <vector>7 using namespacestd;8 Const intmx[9]={0,1,1,-1,-1,2,2,-2,-2};9 Const intmy[9]={0,2,-2,2,-2,1,-1,1,-1};Ten Const intmxn=42000; One intRead () { A     intx=0, f=1;CharCh=GetChar (); -      while(ch<'0'|| Ch>'9'){if(ch=='-') f=-1; ch=GetChar ();} -      while(ch>='0'&& ch<='9') {x=x*Ten-'0'+ch;ch=GetChar ();} the     returnx*F; - } - structedge{intV,nxt,f;} e[mxn<<4]; - inthd[mxn],mct=1; + voidAdd_edge (intUintVintf) { -E[++MCT].V=V;E[MCT].F=F;E[MCT].NXT=HD[U];HD[U]=MCT;return; + } A intn,m; at ints,t; - intD[MXN]; - intid[ About][ About]; - intmp[ About][ About]; - BOOLBFS (intSintt) { -queue<int>Q; inmemset (D,0,sizeofd); -d[s]=1; to Q.push (s); +      while(!Q.empty ()) { -         intu=Q.front (); Q.pop (); the          for(intI=hd[u];i;i=e[i].nxt) { *             intv=e[i].v; $             if(!d[v] &&e[i].f) {Panax Notoginsengd[v]=d[u]+1; - Q.push (v); the             } +         } A     } the     returnD[t]; + } - intDFS (intUintLim) { $     if(u==t)returnLim; $     inttmp,f=0; -      for(intI=hd[u];i;i=e[i].nxt) { -         intv=e[i].v; the         if(d[v]==d[u]+1&&e[i].f) { -tmp=DFS (V,min (LIM,E[I].F));Wuyie[i].f-=tmp; thee[i^1].f+=tmp; -lim-=tmp; Wuf+=tmp; -             if(!lim)returnF; About         } $     } -d[u]=0; -     returnF; - } AInlineintDinic () { +     intres=0; the      while(BFS (s,t)) res+=DFS (s,1e9); -     returnRes; $ } the voidsolve () { the     inti,j; the      for(i=1; i<=n;i++) the       for(j=1; j<=n;j++) -id[i][j]= (I-1) *n+J; in      for(i=1; i<=n;i++) the       for(j=1; j<=n;j++){ the          if(Mp[i][j])Continue; About          if((i+j)%2==0)//White the         { theAdd_edge (S,id[i][j],1); theAdd_edge (Id[i][j],s,0);  +               for(intk=1; k<=8; k++){ -                  intnx=i+mx[k],ny=j+My[k]; the                  if(nx<1|| Nx>n | | ny<1|| Ny>n | | Mp[nx][ny])Continue;BayiAdd_edge (Id[i][j],id[nx][ny],1); theAdd_edge (Id[nx][ny],id[i][j],0); the              } -         } -         Else{//Black theAdd_edge (Id[i][j],t,1); theAdd_edge (T,id[i][j],0); the         } the      } -     return; the } the intMain () the {94Freopen ("knight.in","R", stdin); theFreopen ("Knight.out","W", stdout); theN=read (); m=read (); the     inti,j,u,v;98      for(i=1; i<=m;i++){ AboutU=read (); v=read (); -mp[u][v]=1;//Marker Barriers101     }102s=0; t=n*n+1;103 solve ();104      the     intans=dinic ();106ans=n*n-m-ans;107printf"%d\n", ans);108     return 0;109}

COGS746. [Network Flow 24 questions] Knight Coexistence