# Solve Sudoku using backtracking
def solve(board):
    blank = findEmpty(board)
    if not blank:
        return True
    else:
        row, col = blank

    for i in range(1,10):
        if isValid(board, i, blank):
            board[row][col] = i

            if solve(board):
                return True

            board[row][col] = 0
    return False

# Store in a dictionary the legitimate 
# values for each individual cell
def cacheValidValues(board):
    cache = dict()
    for i in range(9):
        for j in range(9):
            if board[i][j] == 0:
                cache[(i,j)] = allowedValues(board,i,j)
    return cache

def allowedValues(board,row,col):

    numbersList = list()

    for number in range(1,10):

        found = False
        # Check if all row elements include this number
        for j in range(9):
            if board[row][j] == number:
                found = True
                break
        # Check if all column elements include this number
        if found == True:
            continue
        else:
            for i in range(9):
                if board[i][col] == number:
                    found = True
                    break

        # Check if the number is already included in the block
        if found == True:
            continue
        else:
            rowBlockStart = 3* (row // 3)
            colBlockStart = 3* (col // 3)

            rowBlockEnd = rowBlockStart + 3
            colBlockEnd = colBlockStart + 3
            for i in range(rowBlockStart, rowBlockEnd):
                for j in range(colBlockStart, colBlockEnd):
                    if board[i][j] == number:
                        found = True
                        break
        if found == False:
            numbersList.append(number)
    return numbersList

def solveWithCache(board, cache):
    blank = findEmpty(board)
    if not blank:
        return True
    else:
        row, col = blank

    for value in cache[(row,col)]:
        if isValid(board, value, blank):
            board[row][col] = value

            if solveWithCache(board, cache):
                return True

            board[row][col] = 0
    return False

The execution time of above program is : 15.41820478439331 s