My solution attempt for https://news.ycombinator.com/item?id=6639839

flood.rb

#!/usr/bin/env ruby

def flood(*heights)
  stack = []
  max = 0
  volume = 0

  heights.each do |height|
    level = [max, height].min
    count = 0
    while stack.any? and stack.last[0] < level
      h, w = stack.pop
      volume += w * (level - h)
      count += w
    end
    stack.push( [level, count] ) if count > 0
    stack.push( [height, 1] )
    max = [max, height].max
  end
  volume
end

ARGF.each_line do |line|
  nums = line.split(/\s+/).map(&:to_i)
  puts "  => #{flood(*nums)}"
end