Euler 14


  require 'benchmark' 

def euler_chain_size(start)
  length = 0 
  while start > 1 
    start = start%2 == 0 ? start/2 : 3*start+1 
    length += 1 
    if @chains.has_key?(start) 
      length += @chains[start] 
      break 
    end 
  end 
  length 
end 

@chains = {} 
max_chain_size = 0 
max_chain_start = 1 

Benchmark.bm do |x| 
  x.report do 
    1.upto(1000000) do |i| 
      chain_size = euler_chain_size(i) 
      @chains[i] = chain_size 
      if chain_size > max_chain_size 
        max_chain_size = chain_size 
        max_chain_start = i 
      end 
    end 
  end 
  puts "(#{max_chain_start}, #{max_chain_size})" 
end 


  The problem description is here: http://projecteuler.net/index.php?section=problems&id=14

My interest was sparked by: http://diditwith.net/2008/04/03/ApplesAndOranges.aspx
  2008-04-04T00:30:49+00:00
  276
  Ruby
  euler-14
  2
  Euler 14
  
  2008-07-24T07:50:30+00:00
  541
  
    
      require 'benchmark' 

def operation(n)
  return n%2 == 0 ? n/2 : 3*n+1 
end

def recursive(hash, n)
  hash[n] or hash[n] = 1 + recursive(hash, operation(n) )
end

chains = {} 
max_chain_size = 0 
max_chain_start = 1 

Benchmark.bm do |x| 
  x.report do 
    chains[1] = 1
    2.upto(1000000) do |i| 
      chain_size = recursive(chains, i)
      
      if chain_size > max_chain_size 
        max_chain_size = chain_size 
        max_chain_start = i 
      end 
    end 
  end 
  puts "(#{max_chain_start}, #{max_chain_size})" 
end 

      276
      slightly faster, caches more data
      2008-04-06T00:19:24+00:00
      4714
      Ruby
      0
      0
      On Euler 14
      535
      jes5199
      http://jes5199.com
    
    
      array = []
 
(1..1_000_000).each do |x|
  sum = 0
  while x != 1
    sum += 1
    if x % 2 == 0
      x = x / 2
    else
      x = (3 * x) + 1
    end
  end
  array << sum
end
 
puts array.index(array.max) + 1
      276
      From the euler forums
      2008-07-24T07:50:25+00:00
      13708
      Ruby
      0
      0
      On Euler 14
      865
      tyranarchy.myopenid.com