Kattis Eight Queens exercise

Question

Attempting the Eight Queens problem in Python (https://open.kattis.com/problems/8queens).

I've written some code which works for all input I've been able to imagine for the last hour - but the program still fails the Kattis test cases.

It's not very efficient, or well structured, but since the problem shouldn't require speed I didn't really care.

What I'm doing is checking every position, if there is a queen there - I check horizontally, vertically, and diagonally. I figured that it's probably the diagonal checking code that's wrong since the other 2 are very straightforward, but I can't figure it out...

Edit: Request to paste code in question, don't see why but sure:

Edit2: Edited code by adding counter to make sure there are 8 queens.

Edit3: Fixed last bug, code is now working!

import sys
import math

def horizontal(j, row):
    for k in range(8):
        if k == j:
            continue
        if row[k] == '*':
            return False
    return True

def vertical(rows, row , column):
    for i in range(8):
        if i == row:
            continue
        if rows[i][column] == '*':
            return False
    return True

def diagonal(rows, row, column):
    #first diagonal
    current_row = row
    current_col = column

    #go furthest up
    while True:
        if current_col == 0 or current_row == 0:
            break
        current_col-=1
        current_row-=1
    while True:
        if current_row == row and current_col == column:
            if current_col == 7 or current_row == 7:
                break
            current_col += 1
            current_row += 1
            continue
        if rows[current_row][current_col] == '*':
            return False
        if current_col == 7 or current_row == 7:
            break
        current_col += 1
        current_row += 1

    #other diagonal
    current_row = row
    current_col = column
    while True:
        if current_col == 7 or current_row == 0:
            break
        current_col+=1
        current_row-=1
    while True:
        if current_row == row and current_col == column:
            if current_col == 0 or current_row == 7:
                break
            current_col -= 1
            current_row += 1
            continue
        if rows[current_row][current_col] == '*':
            return False
        if current_col == 0 or current_row == 7:
            break
        current_col -= 1
        current_row += 1
    return True

rows = []
for i in range(8):
    rows.append(sys.stdin.readline().rstrip())

valid = True
counter = 0

#for every row:
for row in range(8):
    for column in range(8):
        if rows[row][column] == '*':
            counter += 1
            if not (horizontal(column,rows[row]) and vertical(rows, row, column) and diagonal(rows, row, column)):
                valid = False
                break

    if not valid:
        break
if valid and counter == 8:
    print("valid")
else:
    print("invalid")

Answer 1

You aren't checking to make sure there are exactly 8 queens on the board. Pass in an empty board and your program says it's valid.

num_queens = 0
for row in range(8):
    for column in range(8):
        if rows[row][column] == '*':
            num_queens += 1

...

if num_queens != 8:
    valid = False