Ruby sum is a sober and amazing story

Introduction

The story that sum, which has a reputation for being fast and fast, was really fast

This theme

AtCoder Beginner Contest B - Trapezoid Sum Difficulty: 27

This theme, the sum of arithmetic progressions

The theme is that if you add normally, it will be TLE, so the formula of the sum of arithmetic progressions

S=n(a+b)/2

Let's use. inject(TLE)

ruby.rb

n = gets.to_i
sum = 0
n.times do
  a, b = gets.split.map(&:to_i)
  sum += (a..b).inject(:+)
end
puts sum

Superbly TLE sum(AC)

ruby.rb

n = gets.to_i
sum = 0
n.times do
  a, b = gets.split.map(&:to_i)
  sum += (a..b).sum
end
puts sum

It passes normally. It seems that sum of range uses the formula of sum of arithmetic progressions internally ~~ (appropriate) ~~ Apparently it was true. Please refer to the comment section.

Summary

• Solved ABC 181 B
• sum was fast