POJ-1681 Painter's Problem 高斯消元

//STATUS:C++_AC_16MS_496KB
#include <functional>
#include <algorithm>
#include <iostream>
//#include <ext/rope>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <numeric>
#include <cstring>
#include <cassert>
#include <cstdio>
#include <string>
#include <vector>
#include <bitset>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <list>
#include <set>
#include <map>
using namespace std;
//using namespace __gnu_cxx;
//define
#define pii pair<int,int>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define PI acos(-1.0)
//typedef
typedef long long LL;
typedef unsigned long long ULL;
//const
const int N=300;
const int INF=0x3f3f3f3f;
const int MOD=100000,STA=8000010;
const LL LNF=1LL<<60;
const double EPS=1e-8;
const double OO=1e15;
const int dx[4]={-1,0,1,0};
const int dy[4]={0,1,0,-1};
const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
//Daily Use ...
inline int sign(double x){return (x>EPS)-(x<-EPS);}
template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
template<class T> inline T Min(T a,T b){return a<b?a:b;}
template<class T> inline T Max(T a,T b){return a>b?a:b;}
template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
//End

char ma

;
int A

,B
,vis
,num
;
int T,n;

void getA(int n,int m)
{
int i,j,k,x,y;
mem(A,0);
for(i=0;i<n;i++){
for(j=0;j<m;j++){
A[i*m+j][i*m+j]=1;
for(k=0;k<4;k++){
x=i+dx[k];
y=j+dy[k];
if(x>=0&&x<n && y>=0&&y<m){
A[i*m+j][x*m+y]=1;
}
}
}
}
for(i=0;i<n;i++){
for(j=0;j<m;j++)
A[i*m+j][n*m]=ma[i][j];
}
}

int gauss(int n)
{
int i,j,k,cnt,row,ok,ret,up,free;
for(i=row=0;i<n;i++){
if(!A[row][i]){
for(j=row+1;j<n;j++){
if(A[j][i]){
for(k=i;k<=n;k++)swap(A[row][k],A[j][k]);
break;
}
}
}
if(A[row][i]!=1)continue;
for(j=0;j<n;j++){
if(j!=row && A[j][i]){
for(k=i;k<=n;k++)
A[j][k]^=A[row][k];
}
}
row++;
}
for(i=n-1;i>=row;i--)
if(A[i]
)return -1;
if(row==n){
ret=0;
for(i=0;i<n;i++)if(A[i]
)ret++;
return ret;
}
mem(vis,0);
for(i=k=j=0;i<row;i++){
while(!A[i][j] && j<n){
vis[j]=1;
num[k++]=j++;
}
}
ret=INF;free=n-row;
up=1<<free;
for(k=0;k<up;k++){
for(i=0;i<free;i++)B[num[i]]=(k&(1<<i))?1:0;
for(i=n-1;i>=0;i--){
if(!vis[i])continue;
B[i]=0;
for(j=row;j<n;j++)B[i]^=B[j]*A[i][j];
B[i]^=A[i]
;
}
for(i=cnt=0;i<n;i++)if(B[i])cnt++;
ret=Min(ret,cnt);
}
return ret;
}

int main()
{
//   freopen("in.txt","r",stdin);
int i,j,ans;
scanf("%d",&T);
while(T--)
{
scanf("%d",&n);
for(i=0;i<n;i++){
scanf("%s",ma[i]);
for(j=0;j<n;j++)ma[i][j]=(ma[i][j]=='y'?0:1);
}
getA(n,n);

ans=gauss(n*n);
if(ans>=0)printf("%d\n",ans);
else printf("inf\n");
}
return 0;
}