Why is the output same as the input board ?

Question

board = [
[7,8,0,4,0,0,1,2,0],
[6,0,0,0,7,5,0,0,9],
[0,0,0,6,0,1,0,7,8],
[0,0,7,0,4,0,2,6,0],
[0,0,1,0,5,0,9,3,0],
[9,0,4,0,6,0,0,0,5],
[0,7,0,3,0,0,0,1,2],
[1,2,0,0,0,0,7,4,0],
[0,4,9,2,0,6,0,0,7]
]

def backtrack_solve(board):

find = find_empty(board)

if find is None:
return True
else:
row, col = find

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

if backtrack_solve(board):
return True

board[row][col] = 0

return False

def is_valid(board, num, position):

# To check rows
for i in range(len(board[0])):
if board[position[0]][i] == num and position[1] != i:
return False

# To check columns
for i in range(len(board)):
if board[i][position[1]] == num and position[0] != i:
return False

# To check small-squares
square_x = position[1] // 3
square_y = position[0] // 3

for i in range(square_y * 3, square_y* 3 + 3):
for j in range(square_x * 3, square_x* 3 + 3):
if board[i][j] == num and (i, j) != position:`enter code here`
return False

return True

def print_board(board):
for i in range(len(board)):
if i % 3 == 0 and i != 0:
print("------------------------")
for j in range(len(board[0])):
if j % 3 == 0 and j != 0:
print(" | ", end="")
if j == 8:
print(board[i][j])
else:
print(board[i][j], end=" ")

def find_empty(board):
for i in range(len(board)):
for j in range(len(board[0])):
if board[i][j] == 0:
return (i, j)
return None

print_board(board)
print("\n\n")
backtrack_solve(board)
print_board(board)`enter code here`

Answer 1

board hasn't changed. You need to do

board = backtrack_solve(board)

on the penultimate line.

Answer 2

It's not the case... Since we're passing board as a parameter, it should change.
Check that out Russ
https://code.sololearn.com/c9Z687Gs0qPH/?ref=app

Answer 3

I'm changing the board inside the backtrack_solve, so I don't have to update it further Russ

Answer 4

Can you check it bro... 👑 Prometheus 🇸🇬

Answer 5

This is a backtracking algorithm to solve a sudoku, the code is not on SoloLearn.. Thats why I've shared it in post. Thanx for the advice but it would be great if you've shared its solution too... Or is that you can't solve itManinder $ingh

Answer 6

First of all, tell what this code is doing and always code in the code playground, not in the post section.

Answer 7

'board' inside your backtrack_solve function is not the same as the global variable 'board'. If you want to change thw global 'board' inside the function, you need to declare

global board

inside it. Of course, that would render the board parameter of that function pointless and it would be better to remove it.

def backtrack_solve():
global board
...

Answer 8

Hey SpArShiKa 🎀 ..Help Me Out.. 😂

Answer 9

Nitesh_Babu_Sharma check this code this is backtracking for solve sudoku and try to find where are you going wrong.

https://code.sololearn.com/cbQvETmXZc1k/?ref=app

Answer 10

Nitesh_Babu_Sharma Yep sorry, you are right. So I've finally been able to look at it properly, and I see why it hasn't changed.

I've inserted the line 'print(row, col)' between if backtrack_solve(board): and return True. This will show which row and col number would have been changed since, if backtrack_solve(board) returns False, the number you have just changed is returned to 0.

You should see that no row and column gets output, meaning that your code has simply not found any way of determining any new numbers. (This may be something to do with you having two 7s in the bottom right section of the grid.)

If you want advice on how to fix this, I'd suggest fully commenting your code to describe your algorithm, and posting the direct link to it, rather than pasting the code itself.

Answer 11

Jesus will help you!