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日々の戯れ言

Project Euler 28

Project Euler

Problem28を解きました.

  • Number spiral diagonals

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 the numbers on the diagonals is 101.

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

https://projecteuler.net/problem=26

問題は「1001×1001の螺旋を例と同じ方法で数値を配置したときの,対角線上の数字の総和を求めよ」.

sum = 1
n = 3
i = 0
while (k = 2 * i + 3) <= 1001 do
	sum += n
	for j in 0..2 do
		n += (k - 1)
		sum += n  
	end
	n += (k + 1)
	i += 1
end

p sum

規則性を見つけることができれば,
すんなり解くことができました.