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2016-marzullos-algorithm.rb
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2016-marzullos-algorithm.rb
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# Marzullo’s Algorithm
#
# This one is tricky:
#
# Given a list of events with arrival and departure times, write a program that
# determines the time at which the greatest number events occurred.
#
# For instance, you may have ten employees who arrived at work and departed at
# the times shown below (for instance, employee 9 arrived at 12:00noon and
# departed at 5:00pm):
#
# employee 1 2 3 4 5 6 7 8 9 10
# -- -- -- -- -- -- -- -- -- --
# arrival 10 12 11 13 14 12 9 14 12 10
# departure 15 14 17 15 15 16 13 15 17 18
#
# Then the maximum employee count was at 2:00pm:
#
# 9 | 7 | 1
# 10 | 1 7 10 | 3
# 11 | 1 3 7 10 | 4
# 12 | 1 2 3 6 7 9 10 | 7
# 13 | 1 2 3 4 6 7 9 10 | 8
# 14 | 1 2 3 4 5 6 8 9 10 | 9
# 15 | 1 3 4 5 6 8 9 10 | 8
# 16 | 3 6 9 10 | 4
# 17 | 3 9 10 | 3
# 18 | 10 | 1
#
# There were 9 employees at work at time 14.
#
# Your task is to write a program that determines the start and end times of the
# time block where the greatest number of events occurred.
def time_block_with_most_events(events)
min_t, max_t = events.flatten.minmax
events_on_times = (min_t..max_t).map do |t|
[ t, events.select { |x, y| t.between?(x, y) }.count ]
end
max_events = events_on_times.map { |t, c| c }.max
time_blocks = events_on_times.select { |t, c| c == max_events }.map(&:first)
[max_events] + time_blocks.minmax
end
def test(output, target)
puts "target: #{target}"
puts "output: #{output}"
puts "pass: #{output == target}"
puts
end
arrivals = [10,12,11,13,14,12, 9,14,12,10]
departures1 = [15,14,17,15,15,16,13,15,17,18]
departures2 = [15,15,17,15,15,16,15,15,17,18]
events1 = arrivals.zip(departures1)
events2 = arrivals.zip(departures2)
test time_block_with_most_events(events1), [9, 14, 14]
test time_block_with_most_events(events2), [10, 14, 15]
__END__
Submission
[sourcecode lang="ruby"]
def time_block_with_most_events(events)
min_t, max_t = events.flatten.minmax
events_on_times = (min_t..max_t).map do |t|
[ t, events.select { |x, y| t.between?(x, y) }.count ]
end
max_events = events_on_times.map { |t, c| c }.max
time_blocks = events_on_times.select { |t, c| c == max_events }.map(&:first)
[max_events] + time_blocks.minmax
end
arrivals = [10,12,11,13,14,12, 9,14,12,10]
departures1 = [15,14,17,15,15,16,13,15,17,18]
departures2 = [15,15,17,15,15,16,15,15,17,18]
time_block_with_most_events(arrivals.zip(departures1))
=> [9, 14, 14]
time_block_with_most_events(arrivals.zip(departures2))
=> [10, 14, 15]
[/sourcecode]