POJ 1753 Flip Game 高斯消元法

   高斯很好写，当有自由变元时再枚举一下自由变元就行了。

#include <cstdio>   #include <iostream>#include <string.h>   #include <cmath>#include <vector>#include <algorithm>   using namespace std;typedef long long ll;#define sfint(x) scanf("%d",&x)#define sfint2(x,y) scanf("%d%d",&x,&y)#define sfint3(x,y,z) scanf("%d%d%d",&x,&y,&z)#define sfstr(c) scanf("%s",c)#define sfdl(x) scanf("%lf",&x)#define sfch(c) scanf("%d",&c)#define pfint(x) printf("%d\n",x)#define fr(i,s,n) for(int i=s;i<n;++i)#define _fr(i,n,s) for(int i=n-1;i>=s;--i)#define cl(a) memset(a,0,sizeof(a))int a[20][20];int b[20][20];int de[2][4] = {0,1,0,-1,1,0,-1,0};int best = 20;int x[20];int lim;int freeval(int r){int ret=0;fr(i , 16-lim,16) ret+=a[r][i]*x[i-(16-lim)];return ret%2;}int cal(int cnt){fr(i , 0 ,16-lim) cnt+=a[i][16]^freeval(i);return cnt;}void dfs(int u,int cnt){if (cnt>=best) return ;if(u == lim){best = min(best,cal(cnt));return;}x[u] = 1;dfs(u+1,cnt+1);x[u] = 0;dfs(u+1,cnt);}int gauss(int a[][20],int n){int r,c;for(r = 0, c=0;r<n,c<n;++r,++c){int p = r;fr(i , r+1,n){if(a[i][c] > a[p][c]) p = i;}if (p != r){fr(i , c,n+1){swap(a[p][i],a[r][i]);}}if(a[r][c] == 0){r--;continue;}fr(i , 0,n){if (a[i][c] == 0||i == r) continue;fr(j,c,n+1) a[i][j] = a[i][j]^a[r][j];}}fr(i , r,n) if (a[i][n]) return -1;return n-r;}int main(){#ifdef localfi;#endifchar c[6];fr(i , 0 ,4){sfstr(c);fr(j , 0 ,4){if (c[j] == 'b') a[i*4+j][16] = 1;}}int cnt = 0;fr(i , 0 ,16){cnt+=a[i][16];}if(cnt == 0 || cnt == 16) {puts("0");return 0;}fr(i , 0 ,16){a[i][i] = 1;int r = i/4,c = i%4;fr(d, 0,4){int x = r+de[0][d],y = c+de[1][d];if (x>=0 && x<=3 && y>=0 && y<= 3) a[x*4+y][i] = 1;}}fr(i , 0 ,16){fr(j , 0 ,16) b[i][j] = a[i][j];b[i][16] = a[i][16] ^ 1;}int ans1=gauss(a,16);if(ans1 != -1){lim = ans1;dfs(0,0);}fr(i , 0 ,16){fr(j , 0 ,17) a[i][j] = b[i][j];}ans1=gauss(a,16);if(ans1 != -1){lim = ans1;dfs(0,0);}if(best == 20) puts("Impossible");else printf("%d\n",best);return 0;}