Atcoder Beginner Contest 458 (ABCD)

错过了昨晚史上前四题最简单的ABC，遗憾。在此奉上ABCD Ruby解。
A

s = gets.chomp
n = gets.to_i
puts s[n...-n]

B

h, w = gets.split.map(&:to_i)
num = Array.new(h) { Array.new(w, 0) }
for i in 0...h
  for j in 0...w
    cnt = 0
    if i - 1 >= 0
      cnt += 1
    end
    if i + 1 < h
      cnt += 1
    end
    if j - 1 >= 0
      cnt += 1
    end
    if j + 1 < w
      cnt += 1
    end
    num[i][j] = cnt
  end
end
num.each do |x|
  puts x.join(" ")
end

C

s = gets.chomp.chars
total = 0
len = s.length
s.each_with_index do |s1, i|
  if s1 == "C"
    total += [len - i - 1, i].min + 1
  end
end
puts total

D

require "sorted_containers"
x = gets.to_i
num = SortedContainers::SortedArray.new
num << x
q = gets.to_i
i = 1
q.times do
  a, b = gets.split.map(&:to_i)
  num << a
  num << b
  puts num[i]
  i += 1
end