ELIXIR

Task

Given two strings, A and B, we'll define the similarity of the strings to be the length of the longest prefix common to both strings. For example, the similarity of strings abc and abd is 2, while the similarity of strings aaa and aaab is 3.

For this challenge you'll need to write a function that calculates the sum of similarities of a string with each of its suffixes.

Specification

string_suffix(s)

Counts how many similarities there between a given word and all of its suffixes

Parameters

s: String - Initial word to check against suffixes

Return Value

Integer - Number of matching letters from the word and its suffixes

Example

Let's take a look at the iterations for an example string ababaa:

ababaa ababaa 111111 (6 similarities) ababaa babaa 00000 (0 similarities) ababaa abaa 1110 (3 similarities) ababaa baa 000 (0 similarity) ababaa aa 10 (1 similarity) ababaa a 1 (1 similarity) 

The suffixes of the string are ababaa, babaa, abaa, baa, aa and a. The similarities of each of these strings with the string ababaa are 6, 0, 3, 0, 1, 1 respectively. Thus the answer is 6 + 0 + 3 + 0 + 1 + 1 = 11.

Test

defmodule TestExampleTests do use ExUnit.Case import Challenge, only: [string_suffix: 1]

test "should work for the given example" do assert string_suffix("ababaa") == 11 end

test "should work for a single repeating character" do assert string_suffix("a") == 1 end

test "should work for sets of multiple repeating characters" do assert string_suffix("aa") == 3 end end