AtCoder AGC #017

agc017-a-1.rb

# Submitted answer, AC
n, p_ = gets.chomp.split(" ").map(&:to_i)
a = gets.chomp.split(" ").map(&:to_i)

ne = 0
no = 0
a.each do |i|
  if i.even? then
    ne += 1
  else
    no += 1
  end
end

@fac = Array.new(n)
def fact(n)
  @fac[0] = 1
  (1..n).each do |i|
    @fac[i] = @fac[i-1] * i
  end
end
fact(50)

def comb(n, k)
  return 1 if k == 0
  return @fac[n] / (@fac[n-k] * @fac[k])
end

ans = 0
if p_ == 0 then
  anse = (0..ne).map{|k| comb(ne, k)}.inject(:+)
  anso = 0
  0.step(no, 2){|k| anso += comb(no, k)}
  ans = anse * anso
else
  anse = (0..ne).map{|k| comb(ne, k)}.inject(:+)
  anso = 0
  1.step(no, 2){|k| anso += comb(no, k)}

  ans = anse * anso
end
puts ans

agc017-a-2.rb

n, p_ = gets.chomp.split(" ").map(&:to_i)
a = gets.chomp.split(" ").map(&:to_i)

ne = 0
no = 0
a.each do |i|
  if i.even? then
    ne += 1
  else
    no += 1
  end
end

if no == 0 then
  if p_ == 0
    puts 2 ** n
  else
    puts 0
  end
else
  puts 2 ** (n - 1)
end

agc017-b.rb

n, a, b, c, d = gets.chomp.split(" ").map(&:to_i)

(0...n).each do |k|
  if k * c - (n - 1 - k) * d <= b - a && k * d - (n - 1 - k) * c >= b - a then
    puts "YES"
    exit
  end
end
puts "NO"