Project Euler Problem 28

問題

Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5
spiral is formed as follows:

[21]22 23 24[25]
 20 [7] 8 [9]10
 19  6 [1] 2 11
 18 [5] 4 [3]12
[17]16 15 14[13]

It can be verified that the sum of both diagonals is 101.

What is the sum of both diagonals in a 1001 by 1001 spiral formed in the same way?

ソース

sum = 1
i = 1
a = 2
while i < 1001 * 1001
	4.times{
		sum += (i += a)
	}
	a += 2
end
puts sum

解答

669171001

感想

えっ。。。この問題エグく簡単なんすけど（汗
「1001×1001」の配列使ってやって欲しかったの？？