Sudoko Solver

#include "bits/stdc++.h"
using namespace std;

const int N = 12;
int dp[N][N], maskCol[N], maskRow[N];
int refMask[N][N], matMask[N];
int cnt = 0;

bool check() {
  for (int i = 1; i <= 9; i += 3) {
    for (int j = 1; j <= 9; j += 3) {
      int maskCol = 0;
      for (int r = i; r < i + 3; ++r) {
        for (int c = j; c < j + 3; ++c) {
          if (!dp[r][c]) return 0;
          if (maskCol & (1<<dp[r][c])) return 0;
          maskCol |= (1<<dp[r][c]);
        }
      }
    }
  }
  for (int i = 1; i <= 9; ++i) {
    int maskCol = 0;
    for (int j = 1; j <= 9; ++j) {
      if (maskCol & (1<<dp[i][j])) return 0;
      maskCol |= (1<<dp[i][j]);
    }
  }
  for (int i = 1; i <= 9; ++i) {
    int maskCol = 0;
    for (int j = 1; j <= 9; ++j) {
      if (maskCol & (1<<dp[j][i])) return 0;
      maskCol |= (1<<dp[j][i]);
    }
  }
  // Uncomment to print solution
  // for (int i = 1; i <= 9; i += 1) {
  //  for (int j = 1; j <= 9; j += 1) {
  //   cout << dp[i][j] << " \n"[j==9];
  //   }
  // }
  // exit(0);
  return true;
}
int ans = 0;
void go(int row, int col) {
  ++cnt;
  if (row == 1 and col == 10 && check()) {
    return;
  }
  if (cnt > 5e5) {
    cout << "Seems like infinite loop\n";
    exit(0);
  }
  if (row > 9 or col > 9) return;
  if (dp[row][col]) {
    if (row == 9) go(1,col+1);
    else go(row+1,col);
  }
  else {
    for (int i = 1; i <= 9; ++i) {
      if (!(maskCol[col] & (1<<i)) && !(maskRow[row] & (1<<i))) {
        if (matMask[refMask[row][col]] & (1<<i)) continue;
        maskCol[col] += (1<<i);
        maskRow[row] += (1<<i);
        matMask[refMask[row][col]] += 1<<i;
        dp[row][col] = i;
        if (row == 9) go(1,col+1);
        else go(row+1,col);
        maskCol[col] -= (1<<i);
        maskRow[row] -= (1<<i);
        matMask[refMask[row][col]] -= 1<<i;
        dp[row][col] = 0;
      }
    }
  }
}

int main() {
  int ok = 1;
  for (int i = 1; i <= 9; i += 3) {
    for (int j = 1; j <= 9; j += 3) {
      for (int r = i; r < i + 3; ++r) {
        for (int c = j; c < j + 3; ++c) {
         refMask[r][c] = ok;
        }
      }
      ++ok;
    }
  }
  // go(1,1);

  return 0;
}