Sudoku Solver (hard)

Problem Statement

Write a program to solve a Sudoku puzzle by filling the empty cells.

A sudoku solution must satisfy all of the following rules:

Each of the digits 1-9 must occur exactly once in each row.
Each of the digits 1-9 must occur exactly once in each column.
Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid.

The '.' character indicates empty cells.

Example 1:
Input:

            {'5', '3', '.', '.', '7', '.', '.', '.', '.'},
            {'6', '.', '.', '1', '9', '5', '.', '.', '.'},
            {'.', '9', '8', '.', '

.....

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Mohammed Dh Abbas

· 2 years ago

class Solution:
    def __init__(self):
        self.rows = {i: set() for i in range(9)}
        self.cols = {i: set() for i in range(9)}
        self.boxes = {i: set() for i in range(9)}

    def get_box_number(self, row, col):
        return (row // 3) * 3 + (col // 3)

    def init_used_numbers(self, board):
        for i in range(9):
            for j in range(9):
                if board[i][j] != '.':
                    num = int(board[i][j])
                    self.rows[i].add(num)
                    self.cols[j].add(num)
                    self.boxes[self.get_box_number(i, j)].add(num)

    def is_valid(self, row, col, num):
        box_num = self.get_box_number(row, col)
        return num not in self.rows[row] and num not in self.cols[col] and num not in self.box