Security Challenge #2 Answers

The answer is 6190144.

And here is my Ruby script to calculate the sum of all odd numbers:

puts (1..4976).step(2).inject(0, :+)

!/usr/bin/perl

$f5 = ((0xf+5)*0xf5)+5*0xf+(0xf5/0xf5);
for ($f=0,$fS=1; $fS<$f5; $fS++){$f+=$fS++}
print $f;

python for good measure:

>>> sum = 0
>>> for i in range(1, 4976, 2):
...     sum += i
...
>>> print sum
6190144

Hi Jason,

Nice one, but I still prefer oneliners 😉

>>> sum(range(1, 4976, 2))
6190144

DANGIT @gilliek! :) I was trying to force a list comprehension yesterday but it was not having my += business. Thanks for expanding my toolkit with sum, that's handy. And simple, I love how readable python can be.

sum (1 -> x) = (x*(x+1))/2
sum even (if x is even) (1 -> x) = (x/2*(x/2 +1)
sum odd (1-> x) = (x*(x+1))/2 - (x/2*(x/2 +1))
 = x/2 * ((x+1) - (x/2 +1))
 = x/2 * (x - x/2)

the tcl code is :

% set x 4976
4976
 to convert odd to next even number if number is odd
%set x [expr {($x-1)/2*2+2}]
4976
%set result [expr {$x/2 * ($x - $x/2) }]
6190144