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You also can convert the number to binary string form and match it with a regex: !!num.to_s(2)[/^10*$/]

def gcd a, b return a if b.zero? gcd b, a % b end Avoid ?: when the <return/next/break> if <condition> form can be used.

As a small improvement on top the other answer, you could avoid declaring a double variable by using .divmod to split the digits, like this: def luhn card_no return false if card_no.empty? card_n …

first, :+) end end end end end 0.0013sec vs 2.0sec Making it recursive (break on any depth) could achieve the optimal speed, but such solution becomes not that so easy to read as Ruby …

You can create temporary sorting columns: def sort records, *attrs records.sort_by do |h| h.values_at(*attrs).map do |v| v.nil? ? [2] : [1, v] end end end Here I added columns wit …

To eliminate nested loop you may apply regex checking for invalid symbol from the start -- it would be O(n) + O(n) = O(n): def balanced? string return false if string.length.odd? return false if …

There are three stop conditions depending on the oddity of gaps between the 3rd, 2nd, and 1st most recent number: 0 1 -> 1st (the last one) is the answer 1 0 -> 3rd 1 1 -> 2nd You can run through …

To make Ruby internally use a loop instead of an Array you may want to use 1.upto(10 ** x) that is an Enumerator. But I doubt the "HUGE array" is the performance issue here. … First of all Ruby says to do total = .count{ ... } instead of total = 0; .each{ total += 1 if ... } Then do this thing only once and store in a variable t = i.to_s.split("").sort -- x2 faster Then use …

Based on @tokland code. No need to join array with newline symbol -- #puts does that for you silently: File.open("quijote-words.txt", "w") do |file| file.puts File.read("quijote.txt"). downcase …

Use Kernel#abort: puts "[#{$me}] ERROR: host to destroy must be in first argument. Exit." exit 1 will behave the same as: abort "[#{$me}] ERROR: host to destroy must be in first argument. Exit." …

You may use splat operator instead of .to_a You may use .map.with_index instead of .each_with_index.map You should (bug?) use ... instead of .. def balanced_at? string, index, alphabet = [*"a".."z" …

Never use OOP just because people say it's cool. If you do not know how to apply it, that means you just do not need it in this task. That's it. Forget about OOP. Involving it without much need only m …

I do not match Code Review with this a lot, but I found this problem to be interesting and would solve it without .zip and {}: def isomorphic? a, b each_char_positions = lambda do |string| str …

Using Set instead of Array is faster and checks for presence for you: require "set" def get_random_numbers count, min, max set = Set.new set << rand(min..max) until set.size == count set.to_a …

Array#zip accepts block, so: def fast_power a, b a.zip(b){ |i,j| puts (i**j) % 4211 } end or def fast_power a, b puts a.zip(b).map{ |i,j| (i**j) % 4211 } end But I believe, that competit …