Assigning numbers to an array without using a loop

Question

The task is to assign the n numbers given as input by the user in an array . For Ex : If user gives 10 as input then the generated array should be like this ,

arr[0] = 0
arr[1] = 1
arr[2] = 2
arr[3] = 3
.
.
.
arr[10] = 10 

The code below works fine but i am using a loop to assign this numbers to an array which can prove a lot of run-time during execution if the user gives an input like 10^6 .

puts "enter the number of times you want to test"
times = gets.chomp.to_i
1.upto times do |i|
 puts "enter the total number elements in the array ."
 no = gets.chomp.to_i
 puts "total number of elements are #{no + 1}"
 arr = []
 sum = 0
 0.upto no do |i|
 arr[i] = i
 end
 arr.each_index { |index| print "#{index} " }
 sum = arr.reduce(:+)
 puts "#{sum}" 
end

So , how should i optimize this code for better performance ?

• 200_success: Your title is an extremely generic one that applies to most questions on this site — see How to Ask. Please explain what you mean by "this code". Are you asking about how to sum an array, or are you asking about how rewrite the entire program (which might not involve an array at all)?
• 200_success: The problem is, I'm not sure what you're asking. It's an unclear question.
• Greg Burghardt: The title of a code review should state the purpose of the code. You are free to request specific concerns in the code review itself.
• huzefa biyawarwala: My problem is that the first loop in my program takes way too much running time if a large number is given as input , so what should i do so that it takes less runtime ?

Answer 1

There's no need to #chomp before calling #to_i.

The outer i is never used. In fact, it's confusing, because you introduce an inner i later. If all you want to do is repeat some code, use #times instead of #upto.

no looks like "yes"/"no". By convention, n is a good name for a number, if you don't have any better name for it.

The code would be more efficient if you didn't use any array at all. Just use the series formula:

$$\sum_{i=0}^n i = \dfrac{n (n - 1)}{2}$$

puts "enter the number of times you want to test"
gets.to_i.times do
 puts "enter the total number elements in the array ."
 n = gets.to_i
 puts "total number of elements are #{n + 1}"
 (0..n).each { |i| print "#{i} " }
 puts n * (n - 1) / 2
end

• Flambino: You could also do print (0..n).to_a.join(" ") + " ".
• huzefa biyawarwala: @200_success : where are you assigning the 0 to n numbers to an array which is what i want ? . you are just printing it out . please let me know if there is a better way of assigning the elements in the array for my particular problem.
• 200_success: There is no array because you don't need one to accomplish the task, and it's faster without an array.
• huzefa biyawarwala: Ok . Let's assume we want to assign this 0 to n numbers to an array without using any loop so what should be the approach ?
• 200_success: Why? Please edit the question to clarify.