# loj6007"Network Stream 24 questions" grid Fetch number network flow

Source: Internet
Author: User

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The problem of solving ideas and "" Bzoj "1497 [NOI2006] The biggest profit" the question is similar.

Because if a grid is selected, and the grid of four connected to the grid can not be selected, then we can dye the whole board black and white color and build the edge: All Black squares and source points to build a flow of the number of squares in the edge. All white squares and sinks create a flow that is the edge of the number in the grid. All Black squares with their four-unicom white squares Create a flow of +∞+\infty edges.

Then the new figure to do the smallest cut, that is, the maximum flow, cut the source point and the black square of the edge of the black box to give up the number, cut the white square and the edge of the meeting point to give up the number of white squares, the final checkerboard all the number and minus the maximum flow is the answer.

Attach the AC code:

#include <cstdio> #include <queue> #include <cstring> using namespace std;
const int N=1000,DX[5]={0,1,0,-1,0},DY[5]={0,0,1,0,-1}; struct side{int to,w,nt;}
S[5000];
int N,m,x,st,ed,map[31][31],num,h[n],ans;
Queue <int> que;

int d[n],cur[n];
inline void Add (int x,int y,int W) {s[num]= (side) {y,w,h[x]},h[x]=num++;
S[num]= (side) {x,0,h[y]},h[y]=num++;
} inline bool BFs (int st,int ed) {while (!que.empty ()) Que.pop ();
memset (d,0,sizeof D), D[st]=1,que.push (ST);
while (!que.empty ()) {int P=que.front (); Que.pop ();
for (int i=h[p]; ~i; i=s[i].nt) if (s[i].w&&!d[s[i].to]) D[s[i].to]=d[p]+1,que.push (s[i].to);
if (d[ed]) return 1;
} return 0;
} inline int so (int x,int W) {if (x==ed) return w;
int sum=0,f; for (int &i=cur[x]; ~i; i=s[i].nt) if (s[i].w&&d[s[i].to]==d[x]+1&& (F=so (S[i].to,min (w-sum,s[i
].W))) {s[i].w-=f,s[i^1].w+=f,sum+=f;   if (sum==w) return sum;
} if (!sum) d[x]=0;
return sum;
} #define WZ (x, y) ((x-1) *m+y) int main (void) {scanf ("%d%d", &n,&m), St=0,ed=wz (n,m) +1,memset (h,-1,sizeof h);
for (int i=1; i<=n; ++i) for (int j=1; j<=m; ++j) {scanf ("%d", &x), ans+=x;
if ((i+j)%2==0) {Add (St,wz (I,J), x);
for (int k=1; k<=4; ++k) {int fx=i+dx[k],fy=j+dy[k]; if (fx<1| | fx>n| | fy<1| |
FY&GT;M) continue;
Add (WZ (i,j), WZ (Fx,fy), 2e9);
}} else Add (WZ (i,j), ed,x);
} while (BFS (st,ed)) memcpy (cur,h,sizeof h), Ans-=so (ST,0X7FFFFFFF);
return printf ("%d\n", ans), 0; }
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