Recap
Last time, we discussed procs and how to use them to set default blocks for Ruby methods.
A reminder:
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Insertion Sort – Integers
According to Wikipedia, insertion sort “is a simple sorting algorithm that builds the final sorted array (or list) one item at a time.” Essentially, insertion sort works by keeping track of a sorted sublist, and placing each element in the correct position in that sorted sublist.
First, let’s implement insertion sort with simple integers in ascending order.
So if we implement a method that inserts an element at the correct place in a sorted array, this sort should be easy. If the element is less than or equal to any other element in the sorted array, we should insert the new element before this existing element; otherwise, we should put the new element at the end:
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Again, to sort an array of integers, we just have to iterate through it, placing each element in the sorted sublist:
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This can be refactored as:
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Sort By Condition
But what if we want to sort by an optional, userentered block? ENTER: PROCS.
In Ruby, the spaceship operator a <=> b
compares two items, returning 1 if a > b
, 0 if a == b
, and 1 if a < b
. For example, 3 <=> 2
returns 1, whereas 2 <=> 3
returns 1. 2 <=> 2
returns 0.
Let’s give our sort an optional block variable &block
, so the user can enter his or her own sorting condition. The default condition should be the typical a <=> b
comparison. Now, #sort
becomes:
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This block becomes what we check in #insert_in_right_place
, which becomes:
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So let’s try some examples:
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