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- #!/usr/bin/ruby
- # Daniel "Trizen" Șuteu
- # License: GPLv3
- # https://github.com/trizen
- # https://projecteuler.net/problem=28
- # Runtime: 0.153s
- /*
- 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?
- */
- var N = 1001
- var sum = 1
- for n in (2 .. ceil(N/2)) {
- sum += (n * (16*n - 28) + 16)
- }
- say sum
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