24 lines
911 B
YAML
24 lines
911 B
YAML
title: Evaluate the sum of all amicable pairs under 10000.
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url: http://projecteuler.net/problem=21
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desc: |
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Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
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If d(a) = b and d(b) = a, where a b, then a and b are an amicable pair and each of a and b are called amicable numbers.
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For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
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Evaluate the sum of all the amicable numbers under 10000.
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solution: Bruteforce
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todo: Implement caching in other solutions
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solutions:
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solve.php:
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desc: (Uses a cache to find allready calculated values for d()
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language: php
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solve.rb:
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desc: Basic solution
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language: ruby
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solve.c:
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desc: ANSI C solution (Compiled with TCC)
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language: c
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