bzoj3175tjoi2013 Attack device

3175: [Tjoi2013] Attack device Time Limit:10 Sec Memory limit:128 MB
submit:839 solved:418
[Submit] [Status] [Discuss] Description

Given a 01 matrix, where you can place the attack device in 0 locations. Each attack device (x, y) can be attacked by the word "day" in 8 locations (x-1,y-2), (x-2,y-1), (x+1,y-2), (x+2,y-1), (x-1,y+2), (x-2,y+1), (x+1,y+2), (x+2,y+1)
The maximum number of devices that can be placed in the case of non-attack by the device.
The first line of Input is an integer N, which indicates that the matrix size is n*n. Next n rows each row a length of N of 01 strings, representing the matrix. Output An integer that indicates the maximum number of devices that can be placed if the device is not attacking. Sample Input 3
010
000
100
Sample Output 4 HINT

100% Data n<=200

The maximum point independent set of two graphs

#include <iostream> #include <cstdio> #include <cmath> #include <cstring> #include <cstdlib > #include <algorithm> #define F (I,j,n) for (int. i=j;i<=n;i++) #define D (i,j,n) for (int i=j;i>=n;i--) #
Define ll Long long #define MAXN 40005 using namespace std;
int N,CNT,ANS,HEAD[MAXN],MATCH[MAXN];
int dx[8]={-1,-2,1,2,-1,-2,1,2},dy[8]={-2,-1,-2,-1,2,1,2,1};
BOOL F[205][205],VST[MAXN];
Char s[205]; struct Edge_type{int next,to;}
E[MAXN*8];
	inline int num (int x,int y) {return (x-1) *n+y;} inline void Add_edge (int x,int y) {e[++cnt]= (Edge_type) {head[x],y};
head[x]=cnt;
		} inline bool Dfs (int x) {for (int i=head[x];i;i=e[i].next) {int y=e[i].to;
			if (!vst[y]) {vst[y]=true; if (!match[y]| |
				DFS (Match[y])) {match[y]=x;
			return true;
}}} return false;
	} int main () {scanf ("%d", &n);
		F (i,1,n) {scanf ("%s", s+1);
	F (j,1,n) f[i][j]=s[j]== ' 0 '; } f (I,1,n) f (j,1,n) if (f[i][j]&& (i+j)%2) F (k,0,7) {int x=i+dx[k],y=j+DY[K]; if (x<1| | y<1| | x>n| |
		Y>n) continue;
		if (!f[x][y]) continue;
	Add_edge (Num (i,j), num (x, y));
	} f (I,1,n) f (j,1,n) if (f[i][j]) ans++;
		F (i,1,n) f (j,1,n) if (f[i][j]&& (i+j)%2) {memset (vst,false,sizeof (VST));
	if (DFS (num (i,j))) ans--;
	} printf ("%d\n", ans);
return 0;
 }