AtCoder Beginner Contest D - Powerful Discount Tickets Difficulty: 826
This theme, priority queue
This time, we are using the Priority Queue in it.
The standard library has a priority queue for Java and Python, but it is a long-awaited library because it is not in Ruby.
D - Powerful Discount Tickets
ruby.rb
# frozen_string_literal: true
# Priority Queue
# Reference: https://github.com/python/cpython/blob/master/Lib/heapq.py
class PriorityQueue
# By default, the priority queue returns the maximum element first.
# If a block is given, the priority between the elements is determined with it.
# For example, the following block is given, the priority queue returns the minimum element first.
# `PriorityQueue.new { |x, y| x < y }`
#
# A heap is an array for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for all k, counting elements from 0.
def initialize(array = [], &comp)
@heap = array
@comp = comp || proc { |x, y| x > y }
heapify
end
attr_reader :heap
# Push new element to the heap.
def push(item)
shift_down(0, @heap.push(item).size - 1)
end
alias << push
alias append push
# Pop the element with the highest priority.
def pop
latest = @heap.pop
return latest if empty?
ret_item = heap[0]
heap[0] = latest
shift_up(0)
ret_item
end
# Get the element with the highest priority.
def get
@heap[0]
end
alias top get
# Returns true if the heap is empty.
def empty?
@heap.empty?
end
private
def heapify
(@heap.size / 2 - 1).downto(0) { |i| shift_up(i) }
end
def shift_up(pos)
end_pos = @heap.size
start_pos = pos
new_item = @heap[pos]
left_child_pos = 2 * pos + 1
while left_child_pos < end_pos
right_child_pos = left_child_pos + 1
if right_child_pos < end_pos && @comp.call(@heap[right_child_pos], @heap[left_child_pos])
left_child_pos = right_child_pos
end
# Move the higher priority child up.
@heap[pos] = @heap[left_child_pos]
pos = left_child_pos
left_child_pos = 2 * pos + 1
end
@heap[pos] = new_item
shift_down(start_pos, pos)
end
def shift_down(star_pos, pos)
new_item = @heap[pos]
while pos > star_pos
parent_pos = (pos - 1) >> 1
parent = @heap[parent_pos]
break if @comp.call(parent, new_item)
@heap[pos] = parent
pos = parent_pos
end
@heap[pos] = new_item
end
end
HeapQueue = PriorityQueue
n, m = gets.split.map(&:to_i)
a = gets.split.map(&:to_i)
h = PriorityQueue.new(a)
m.times do
x = h.pop
h.push(x / 2)
end
puts h.heap.sum
ruby.rb
# frozen_string_literal: true
# Priority Queue
# Reference: https://github.com/python/cpython/blob/master/Lib/heapq.py
class PriorityQueue
# By default, the priority queue returns the maximum element first.
# If a block is given, the priority between the elements is determined with it.
# For example, the following block is given, the priority queue returns the minimum element first.
# `PriorityQueue.new { |x, y| x < y }`
#
# A heap is an array for which a[k] <= a[2*k+1] and a[k] <= a[2*k+2] for all k, counting elements from 0.
def initialize(array = [], &comp)
@heap = array
@comp = comp || proc { |x, y| x > y }
heapify
end
attr_reader :heap
# Push new element to the heap.
def push(item)
shift_down(0, @heap.push(item).size - 1)
end
alias << push
alias append push
# Pop the element with the highest priority.
def pop
latest = @heap.pop
return latest if empty?
ret_item = heap[0]
heap[0] = latest
shift_up(0)
ret_item
end
# Get the element with the highest priority.
def get
@heap[0]
end
alias top get
# Returns true if the heap is empty.
def empty?
@heap.empty?
end
private
def heapify
(@heap.size / 2 - 1).downto(0) { |i| shift_up(i) }
end
def shift_up(pos)
end_pos = @heap.size
start_pos = pos
new_item = @heap[pos]
left_child_pos = 2 * pos + 1
while left_child_pos < end_pos
right_child_pos = left_child_pos + 1
if right_child_pos < end_pos && @comp.call(@heap[right_child_pos], @heap[left_child_pos])
left_child_pos = right_child_pos
end
# Move the higher priority child up.
@heap[pos] = @heap[left_child_pos]
pos = left_child_pos
left_child_pos = 2 * pos + 1
end
@heap[pos] = new_item
shift_down(start_pos, pos)
end
def shift_down(star_pos, pos)
new_item = @heap[pos]
while pos > star_pos
parent_pos = (pos - 1) >> 1
parent = @heap[parent_pos]
break if @comp.call(parent, new_item)
@heap[pos] = parent
pos = parent_pos
end
@heap[pos] = new_item
end
end
HeapQueue = PriorityQueue
gets
a = gets.split.map(&:to_i)
h = PriorityQueue.new(a)
while h.heap.size > 1
u = h.pop
v = h.pop
h.push(u - 1) if u - 1 > 0
h.push(v - 1) if v - 1 > 0
end
if h.heap.size.zero?
puts 0
else
puts h.pop - 1
end
D --Powerful Discount Tickets has a nice execution time of 880-> 395 ms.
Referenced site ac-library-rb - GitHub
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