我對歐拉＃58項目的這個答案的錯誤在哪裏？

Question

我正在解決項目Euler question 58。這裏的正方形是從1開始，並以下面的方式盤旋逆時針（這裏是邊長等於7創建：

37 36 35 34 33 32 31 
38 17 16 15 14 13 30 
39 18 5 4 3 12 29 
40 19 6 1 2 11 28 
41 20 7 8 9 10 27 
42 21 22 23 24 25 26 
43 44 45 46 47 48 49 

的問題是找出當我們不斷在廣場周圍盤旋，當比值對角線上的素數和對角線上的數字量小於0.10。

我確信我的解決方案使用下面的代碼（請參閱代碼註釋以獲得澄清），但該網站聲明答案錯誤時我正在輸入它

require 'prime' 

# We use a mathematical derivation of the corner values, keep increasing the value till we find a ratio smaller 
# than 0.10 and increase the grid_size and amount of numbers on diagonals each iteration 

side_length = 3 # start with grid size of 3x3 so that we do not get into trouble with 1x1 grid 
prime_count = 3 # 3, 5, 7 are prime and on a diagonal in a 3x3 grid 
diagonal_size = 5 
prime_ratio = 1 # dummy value bigger than 0.10 so we can start the loop 

while prime_ratio >= 0.10 
    # Add one to prime count for each corner if it is prime 
    # Corners are given by n2 (top left), n2-n+1, n2-2n+2, and n2-3n+3 
    prime_count += 1 if (side_length**2).prime? 
    prime_count += 1 if (side_length**2-side_length+1).prime? 
    prime_count += 1 if (side_length**2-2*side_length+2).prime? 
    prime_count += 1 if (side_length**2-3*side_length+3).prime? 
    # Divide amount of primes counted by the diagonal length to get prime ratio 
    prime_ratio = prime_count/diagonal_size.to_f 
    # Increase the side length by two (full spiral) and diagonal size by four 
    side_length += 2 and diagonal_size += 4 
end 

puts side_length-2 #-2 to account for last addition in while-loop 

# => 26612 

這可能是錯誤的，網站是正確的。我現在陷入了這個問題很長一段時間。任何人都可以指出我的錯誤？

Answer 1

side_length += 2 and diagonal_size += 4應該在循環的開始處。

無法檢查，我沒有安裝ruby，但我可以在我的python解決方案上重現相同的問題。