sudoku-solver.cpp

bool isValid(vector < vector < char >> & board, int row, int col, char ch) {
  for (int i = 0; i < 9; i++) {
    if (board[i][col] == ch) {
      return false;
    }
    if (board[row][i] == ch) {
      return false;
    }
    if (board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == ch) {
      return false;
    }
  }
  return true;
}

bool solve(vector < vector < char >> & board) {
  for (int i = 0; i < board.size(); i++) {
    for (int j = 0; j < board[0].size(); j++) {
      if (board[i][j] == '.') {
        for (char ch = '1'; ch <= '9'; ch++) {
          if (isValid(board, i, j, ch)) {
            board[i][j] = ch;
            if (solve(board) == true) {
              return true;
            }
            board[i][j] = '.';
          }
        }
        return false;
      }
    }
  }
  return true;
}

void solveSudoku(vector < vector < char >> & board) {
  solve(board);
}