# Purpose

Let’s try to put together a sort algorithm by actually writing code. Let’s try the language with Ruby.

To sort, sort the numbers given as input in ascending order.

## Bubble sort

Bubble sort repeats the operation of “comparing and swapping two adjacent numbers from right to left in the sequence”. If the process is repeated once for a sequence of numbers, the smallest number will be in the first position of the array. It is possible to sort by going around the number of elements.

#### `bubble.rb`

``````
def bubble_sort(array)
length = array.length
(length-1).times do |round|
(length-1-round).times do |n|
if array[length-n-1] <array[length-n-2]
smaller = array[length-n-1]
array[length-n-1] = array[length-n-2]
array[length-n-2] = smaller
end
end
end
array
end

array = [2, 3, 13, 7, 8, 9, 11, 1, 5]
bubble_sort(array) #=> [1, 2, 3, 5, 7, 8, 9, 11, 13]
``````

Contents of bubble sort function ・Get the length of array array by length (first line) ・(Length-1) round ends swapping (second line)

• In the nth round, (length-n-1) times are compared and the process of swapping is performed (3rd line) ・If the value on the left is greater than the value on the right, swap them (lines 4-7). The number of comparisons is (length-1) + (length-2) + … + 1 = (length)^2 / 2.

## Selection sort

For selective sorting, the operation of “searching for the minimum value in the sequence of numbers and replacing it with the leftmost number” is repeated.

#### `selection.rb`

``````
def selection_sort(array)
length = array.length
(length-1).times do |round|
min = round + 1
round.upto(length-1) do |n|
if array[n] <array[min]
min = n
end
end
min_number = array[min]
array[min] = array[round]
array[round] = min_number
end
array
end
``````

Get the smallest index number and replace it after searching. Same as bubble sort, the number of comparisons is (length)^2/2.

# Postscript

Next, I’ll summarize insert sort, heap sort, merge sort, quick sort, and bucket sort.

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