func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 25, mod = 1e9 + 7;   int a[N][N], used[N][N], cur, first, n, m, k;   long long ans;   int count(int x) {     int ans = 0;     for (; x; x -= x & -x) ans++;     return ans;   }   void dfs(int x, int y) {     if (x == n) {       int p = count(cur & ~first), q = count(((1 << k) - 1) & ~first);       long long curans = 1;       while (p--) {         curans = (curans * q) % mod;         q--;       }       ans = (ans + curans) % mod;       return;     }     int nx = x, ny = y + 1;     if (ny == m) {       nx++;       ny = 0;     }     if (a[x][y]) {       dfs(nx, ny);       return;     } else {       bool flag = true;       int can = (1 << k) - 1;       can &= ~used[x][y];       for (int i = 0; (1 << i) <= can; i++) {         if (!((can >> i) & 1)) continue;         bool preused[N][N], preusedcur;         preusedcur = true;         memset(preused, false, sizeof(preused));         if (!((cur >> i) & 1)) {           if (flag)             flag = false;           else             continue;           preusedcur = false;         }         cur |= 1 << i;         for (int px = x; px < n; px++)           for (int py = y; py < m; py++) {             if ((used[px][py] >> i) & 1)               preused[px][py] = true;             else               used[px][py] |= 1 << i;           }         dfs(nx, ny);         if (!preusedcur) cur &= ~(1 << i);         for (int px = x; px < n; px++)           for (int py = y; py < m; py++) {             if (!preused[px][py]) used[px][py] &= ~(1 << i);           }       }     }   }   int main() {     scanf( %d%d%d , &n, &m, &k);     if (n + m - 1 > k) {       printf( 0 n );       return 0;     }     for (int i = 0; i < n; i++)       for (int j = 0; j < m; j++) {         scanf( %d , &a[i][j]);         if (a[i][j]) {           first |= 1 << a[i][j] - 1;           if ((used[i][j] >> a[i][j] - 1) & 1) {             printf( 0 n );             return 0;           }           for (int r = 0; r < n; r++)             for (int c = 0; c < m; c++) {               if (r <= i && c <= j || r >= i && c >= j)                 used[r][c] |= 1 << a[i][j] - 1;             }         }       }     cur = first;     dfs(0, 0);     printf( %d n , ans);     return 0;   }   