Posted by oxaric on November 24, 2008
It uses Ruby.
Click to directly download euler-solution-21.rb
# filename 'euler-solution-21.rb'
# By: Louis Casillas, oxaric@gmail.com
# Euler Problem #21
# Evaluate the sum of amicable numbers under 10000
# d(n) = sum of the divisors of n
# Numbers are amicable if d(a) = b and d(b) = a, where a is not b
def d( num )
sum = 0
i = 1
half_num = ( num / 2 )
if (num % 2) == 0
adder = 1
else
adder = 2
end
while i <= half_num
if (num % i) == 0
sum += i
end
i += adder
end
sum
end
UPTO = 10000
array_of_used_numbers = Array.new()
sum = 0
for i in (2...UPTO)
a = d(i)
b = d(a)
if (a != b) && (i == b)
is_new_one = true
for j in (0...array_of_used_numbers.size)
if (i == array_of_used_numbers[j]) || (b == array_of_used_numbers[j])
is_new_one = false
end
end
if is_new_one
array_of_used_numbers.insert( 0, i )
array_of_used_numbers.insert( 0, a )
array_of_used_numbers.insert( 0, b )
sum += ( i + a )
end
end
end
puts "The sum is: " + sum.to_s
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This entry was posted on November 24, 2008 at 8:55 and is filed under Programming, Project Euler, Ruby.
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