Sorting quickly
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module QuickSort | |
def sort(array, options = {}) | |
start_index = options[:start_index] || 0 | |
end_index = options[:end_index] || array.length - 1 | |
unless start_index >= end_index | |
# Randomly choose a pivot and swap with the end index. | |
pivot_index = rand(end_index - start_index + 1) + start_index | |
temp = array[end_index] | |
array[end_index] = array[pivot_index] | |
array[pivot_index] = temp | |
# Separate the array into elements less than or equal to the pivot, the pivot, and | |
# elements greater than the pivot. | |
# Note that this means the pivot will be in the correct place. | |
last_less_index = start_index - 1 | |
(start_index...end_index).each do |i| | |
if array[i] <= array[end_index] | |
last_less_index += 1 | |
temp = array[i] | |
array[i] = array[last_less_index] | |
array[last_less_index] = temp | |
end | |
end | |
last_less_index += 1 | |
temp = array[end_index] | |
array[end_index] = array[last_less_index] | |
array[last_less_index] = temp | |
# Sort the elements less than or equal to the pivot. | |
sort(array, start_index: start_index, end_index: last_less_index - 1) | |
# Sort the elements greater than the pivot. | |
sort(array, start_index: last_less_index + 1, end_index: end_index) | |
end | |
end | |
end |
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require './quicksort' | |
require 'test/unit' | |
class QuickSortTest < Test::Unit::TestCase | |
include QuickSort | |
def test_sort | |
# Empty array. | |
array = [] | |
sort(array) | |
assert(array.empty?) | |
# Single array. | |
array = [1] | |
sort(array) | |
assert_equal(1, array[0]) | |
# Two elements. | |
array = [1, 2] | |
sort(array) | |
assert_equal(1, array[0]) | |
assert_equal(2, array[1]) | |
# Sorted array. | |
array = [1, 2, 3, 4, 5, 6] | |
sort(array) | |
assert_equal(1, array[0]) | |
assert_equal(2, array[1]) | |
assert_equal(3, array[2]) | |
assert_equal(4, array[3]) | |
assert_equal(5, array[4]) | |
assert_equal(6, array[5]) | |
# Reverse sorted array. | |
array = [6, 5, 4, 3, 2, 1] | |
sort(array) | |
assert_equal(1, array[0]) | |
assert_equal(2, array[1]) | |
assert_equal(3, array[2]) | |
assert_equal(4, array[3]) | |
assert_equal(5, array[4]) | |
assert_equal(6, array[5]) | |
# Arbitrary array. | |
array = [5, 2, 4, 1, 6, 3] | |
sort(array) | |
assert_equal(1, array[0]) | |
assert_equal(2, array[1]) | |
assert_equal(3, array[2]) | |
assert_equal(4, array[3]) | |
assert_equal(5, array[4]) | |
assert_equal(6, array[5]) | |
end | |
end |
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