SudokuSolver.py

grid =[
    [6,5,0,8,7,3,0,9,0],
    [0,0,3,2,5,0,0,0,8],
    [9,8,0,1,0,4,3,5,7],
    [1,0,5,0,0,0,0,0,0],
    [4,0,0,0,0,0,0,0,2],
    [0,0,0,0,0,0,5,0,3],
    [5,7,8,3,0,1,0,2,6],
    [2,0,0,0,4,8,9,0,0],
    [0,9,0,6,2,5,0,8,1]
    ]
K = len(grid)

def print_sudoku():
    # Print Sudoku
    for i in range(K):
        if i % 3 == 0 and i!= 0:
            print('----------------------')
        for j in range(K):
            if j % 3 == 0 and j != 0:
                print(" | ", end='')
            if j == 8:
                print(grid[i][j])
            else:
                print(grid[i][j],end=' ')


def missing_num(row, col):
    flag = 0
    for i in range(K):
        for j in range (K):
            #cell is unassigned
            if grid[i][j] == 0:
                row = i
                col = j
                flag = 1
                a = [row, col, flag]
                return a
    a = [-1, -1, flag]
                                      
    return a                                 

#print(missing_num(0,0))

def is_safe(n,r,c):
    # row 
    for i in range(K):
        if grid[r][i] == n:
            return False 

    #column
    for i in range(K):
        if grid[i][c] == n:
            return False

    row_start = (r//3)*3
    col_start = (c//3)*3
    #checking submatrix
    for i in range(row_start,row_start+3):
        for j in range(col_start,col_start+3):
            if grid[i][j]==n:
                return False
    return True

def solver():
    row = 0
    col = 0
    a = missing_num(row, col)
    if a[2] == 0:
        return True
    row = a[0]
    col = a[1]
    #number between 1 to 9
    for i in range(1,K+1):
        if is_safe(i, row, col):
            grid[row][col] = i
            if solver():
                return True
            grid[row][col]=0
    return False

if solver():
    print_sudoku()
else:
    print('Check Your Sudoku')