poj1681 Painter's Problem高斯消元

链接http://poj.org/problem?id=1681

View Code

 1 #include <stdio.h> 
 2 #include <string.h>
 3 #include <algorithm>
 4 #include <cmath>
 5 using namespace std;
 6 int d[230][230], N, M;
 7 char s[16][16]; 
 8 void solve( int n)
 9 {
10     int x[230],m[20], t, ans=1000, temp;
11     t=M-n;
12     for( int i=1; i<=pow( 2, t ); ++i ){
13         memset( x, 0, sizeof x  );
14         for(int j=0; j<t; ++j){
15             m[j]=(i&(1<<j));
16             if(m[j]){
17                 x[n+j]=1;
18             }    
19         }
20         temp=0;
21         for( int p=n+1;p>=1;--p ){
22             for(int k=i+1;k<=M;++k){
23                     x[p]^=( x[k]&&d[p][k] );
24                 
25             }
26             x[p]^=d[p][M+1];
27             if( x[p])
28                 temp++;
29         } 
30         ans=min( ans, temp );
31     }
32     printf( "%d\n", ans );
33 }
34 void Gauss(  )
35 {
36     int i=1, j, k , p, t;
37     for(j=1; j<=M; ++j){
38         for(p=i; p<=M; ++p){
39             if(d[p][j])break;
40         }
41         if( p>M )continue;
42         if(p!=i){
43             for(k=j;k<=M+1; ++k){
44                 t=d[p][k],d[p][k]=d[i][k],d[i][k]=t;
45             }    
46         }
47         for(p=i+1; p<=M; ++p){
48             if( d[p][j] ){
49                 for( k=j; k<=M+1; ++k ){
50                     d[p][k]^=d[i][k];
51                 }
52             }
53         }
54         ++i;
55     }
56     for( p=i; p<=M; ++p ){
57         if( d[p][M+1] ){
58             puts("inf");
59             return;
60         }
61     }    
62     solve( i-1 );
63 }
64 int main( )
65 {
66     int T; 
67     scanf("%d", &T );
68     while( T --) {
69         scanf( "%d", &N );
70         M=N*N;
71         for( int i=0; i<N; ++ i ){
72             scanf( "%s", s[i] ); 
73         } 
74         memset( d, 0, sizeof d );
75         for( int i=1; i<=M; ++ i )
76             d[i][i]=1;
77         for( int i=0; i<N; ++i ){
78             for( int j=0;j<N; ++j ){
79                 if( s[i][j]=='w' ) d[i*N+j+1][M+1]=1;
80                 
81                 if( i>0 )d[(i-1)*N+j+1][i*N+j+1]=1;
82                 if( j>0 )d[i*N+j][i*N+j+1]=1;
83                 if( i<N-1 )d[(i+1)*N+j+1][i*N+j+1]=1;
84                 if( j<N-1 )d[i*N+j+2][i*N+j+1]=1;        
85             } 
86         }
87         Gauss( ); /*
88         for( int i=1; i<=M; ++i ){
89             for(int j=1;j<=M; ++ j ){
90                 printf( "%d ", d[i][j] );
91             }
92             puts( "" );
93         }*/
94     } 
95     return 0;    
96 }