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@ubermajestix ubermajestix/README.md
Last active Dec 27, 2015

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Twitter Interview Question

This code visualizes the solution to this Twitter interview question.

My first solution only looked at immediate neighbors to figure out if you're in a trough that will collection water. The clever part is considering all values to the left and right of you, not immediate neighbors. My naive solution to [5,1,5] was pretty close, but as I expanded to more complex problems, considering your neighbors wasn't enough and my solution began to bloat. Looking at this answer gave me the insight to strip down my solution.

Once I had it solved I went back and built the simple solution display.

To run the tests simply run $> ruby -Itest rain_test.rb

# encoding: utf-8
class Rain
attr_reader :land, :volume
def initialize(land)
@land = land
@volume = 0
end
# from where you are you want to know if you're in a trough
# Moving left find the largest value, moving right find the largest value
# take the lesser of the two and subtract from yourself.
def calculate_volume
land.each_with_index{|h, index|
left = land[0..index].max
right = land[index..-1].max
if h < left && h < right
@volume += [left,right].min - h
end
}
return @volume
end
def print_solution
puts "\nBoard for #{land.inspect}"
max = land.max
max.times do |n|
n = max - n
l = []
land.each_with_index do |h, index|
left = land[0..index].max
right = land[index..-1].max
if h < left && h < right
if n <= [left,right].min && n > h
l << ""
else
l << "|" if n <= h
l << " " if h < n
end
else
l << "|" if n <= h
l << " " if h < n
end
end
puts l.join
end
puts "_" * land.length
puts "Volume: #{calculate_volume}"
end
end
require 'minitest/autorun'
require_relative 'rain'
describe Rain do
specs = {
[1,2,3,4,5,4,5,3] => 1,
[2,1,2,3,4,2] => 1,
[5,1,5] => 4,
[2,7,2,1,7,4] => 11,
[2,8,2,1,7,4] => 11,
[2,7,2,-1,4,9] => 5+8+3,
[5,1,0,1] => 1,
[2,5,1,2,3,4,7,7,6,3,5] => 12
}
specs.each do |array, expected|
it "should provide #{expected} for #{array}" do
rain = Rain.new(array)
rain.print_solution
assert_equal expected, rain.volume, "Failed for #{array.inspect}"
end
end
end
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