AtCoder #ABC 034

abc034-a.rb

x, y = gets.chomp.split(" ").map(&:to_i)
if x < y then
  puts "Better"
else
  puts "Worse"
end

abc034-b.rb

n = gets.chomp.to_i
if n.even? then
  puts n - 1
else
  puts n + 1
end

abc034-c.rb

w, h = gets.chomp.split.map(&:to_i)
w-=1
h-=1

MOD = 1_000_000_007

def fact(n)
  ans = 1
  2.upto(n).each do |i|
    ans *= i
    ans = ans % MOD
  end
  return ans
end

def calc(a, b, p)
  if b == 0 then
    return 1
  elsif b.even? then
    d = calc(a, b/2, p)
    return (d * d) % p
  else
    return (a * calc(a, b - 1, p)) % p
  end
end

def comb(n, k)
  mul = fact(n+k)
  div = (fact(n) * fact(k)) % MOD
  inverse = calc(div, MOD - 2, MOD)
  return (mul * inverse) % MOD
end

puts comb(w, h)

abc034-d-greedy.rb

n, k = gets.chomp.split(" ").map(&:to_i)
a = []
n.times do 
  w, p = gets.chomp.split(" ").map(&:to_f)
  solt = w * p
  a << [w, p, solt]
end
a = a.sort_by{|x| -x[1]}
amax = a.shift
  
pmax = 0
pi = 0
w = 0
solt = 0
  
(k-1).times do
  (n-1).times do |i|
    tmp = (amax[2] + a[i][2]) / (amax[0] + a[i][0])
    if tmp > pmax then
      pmax = tmp
      w = amax[0] + a[i][0]
      solt = amax[2] + a[i][2]
      pi = i
    end
  end
  a.delete_at(pi)
  i = (0...a.size).bsearch{|x| a[x][1] < pmax}
  a.insert(i, [w, pmax, solt])
  amax = a.shift
  n -= 1
  pmax = 0
end
puts amax[1]

abc034-d.rb

n, k = gets.chomp.split.map(&:to_i)
a = []
n.times do 
  w, p = gets.chomp.split(" ").map(&:to_f)
  a << [w, p]
end

class Hello
  def initialize(n, k, a)
    @n = n
    @k = k
    @a = a
    @lower = 0.0
    @upper = 100.0
  end

  attr_accessor :lower

  def check(mid)
    ans = 0
    solt = []
    @n.times do |i|
      solt << @a[i][0] * (@a[i][1] - mid)
    end
    solt.sort!
    solt.pop(@k).each do |i|
      ans += i
    end
    if (ans >= 0) then
      return true
    else
      return false
    end
  end
  
  def calc()
    mid = (@lower + @upper) / 2
    if self.check(mid) then
      @lower = mid
    else
      @upper = mid
    end
  end
end

x = Hello.new(n, k, a)

100.times do
  x.calc()
end

puts x.lower