[bzoj1923]外星千足虫[高斯消元]

高斯消元解异或方程组

 #include <iostream>
 #include <algorithm>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <cmath>
 #include <ctime>
 #include <bitset>

 using namespace std;

 int n,m,Ans;
 char    str[];
 bitset<>  a[];

 void    Gauss()
 {
     int i,j,k,cur=;
     for(i=;i<=n;++i)
     {
         cur++;j=cur;
         while(!a[j][i] && j<=m)j++;
         if(j==m+){Ans=-;return ;}
         else    Ans=max(Ans,j);
         if(j!=cur)swap(a[j],a[cur]);
         for(k=;k<=m;++k)
             if(a[k][i] && k!=cur)a[k]^=a[cur];
     }
     return ;
 }

 int main()
 {
     int i,j;

     scanf("%d%d",&n,&m);
     for(i=;i<=m;++i)
     {
         scanf("%s",str+);
         for(j=;j<=n;++j)a[i][j]=str[j]-;
         scanf("%s",str+);
         a[i][n+]=str[]-;
     }

     Gauss();

     if(Ans==-){printf("Cannot Determine\n");goto End;}
     printf("%d\n",Ans);
     for(i=;i<=n;++i)
         printf("%s\n",a[i][n+]?"?y7M#":"Earth");
 End:
     return ;
 }