代码如下:
#include <cstdlib> #include <cstring> #include <cstdio> #include <algorithm> #define TO(x, y) (x-1)*N+y using namespace std; char G[30][30]; int dir[4][2] = {1, 0, -1, 0, 0, 1, 0, -1}, N; int C; inline bool judge(int x, int y) { if (x < 1 || x > N || y < 1 || y > N) { return false; } return true; } void swap(int &a, int &b) { int t = a; a = b; b = t; } struct Matrix { int a[300][300]; void init() { int xx, yy, k, pos; memset(a, 0, sizeof (a)); for (int i = 1; i <= N; ++i) { for (int j = 1; j <= N; ++j) { k = TO(i, j); a[k][k] = 1; for (int d = 0; d < 4; ++d) { xx = i + dir[d][0], yy = j + dir[d][1]; if (judge(xx, yy)) { pos = TO(xx, yy); a[pos][k] = 1; } } } } } void rswap(int x, int y, int s) { for (int j = s; j <= C+1; ++j) { swap(a[x][j], a[y][j]); } } void relax(int x, int y, int s) { for (int j = s; j <= C+1; ++j) { a[y][j] ^= a[x][j]; } } }M; void solve(int R) { int f1 = 0, x1[300], t1, ans1 = 0x3fffffff; for (int i = R + 1; i <= C; ++i) { if (M.a[i][C+1]) f1 = 1; } if (f1) { puts("inf"); return; } for (int s = 0; s < 1<<(C-R); ++s) { t1 = 0; memset(x1, 0, sizeof (x1)); for (int i = 0; i < (C-R); ++i) { x1[R+i+1] = s & (1 << i) ? 1 : 0; if (x1[R+i+1]) ++t1; } for (int i = R; i >= 1; --i) { for (int j = i + 1; j <= C; ++j) { x1[i] ^= (x1[j] * M.a[i][j]); } x1[i] ^= M.a[i][C+1]; if (x1[i]) ++t1; } ans1 = min(ans1, t1); } printf("%d\n", ans1); } void Gauss() { int i = 1, k; for (int j = 1; j <= C; ++j) { // 枚举上三角矩阵的对角线 for (k = i; k <= C; ++k) { if (M.a[k][j]) break; } if (k > C) continue; if (k != i) { // 如果该行就是第首行,那么我们直接进行消元,否则交换行,使得第一行为单位1 M.rswap(k, i, j); } for (k = i + 1; k <= C; ++k) { // 从下一行开始进行消元 if (M.a[k][j]) { M.relax(i, k, j); } } ++i; } solve(i - 1); } int main() { int T; scanf("%d", &T); while (T--) { scanf("%d", &N); C = N*N; M.init(); for (int i = 1; i <= N; ++i) { scanf("%s", G[i] + 1); } for (int i = 1; i <= N; ++i) { for (int j = 1; j <= N; ++j) { M.a[TO(i, j)][C+1] = G[i][j] == 'w'; } } Gauss(); } return 0; }