shmibs's solution

to Matching Brackets in the Crystal Track

Published at Dec 29 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

Bracket Push

Given a string containing brackets [], braces {}, parentheses (), or any combination thereof, verify that any and all pairs are matched and nested correctly.

Setup

Follow the setup instructions for Crystal here:

http://exercism.io/languages/crystal

More help installing can be found here:

http://crystal-lang.org/docs/installation/index.html

Making the Test Suit Pass

Execute the tests with:

\$ crystal spec

In each test suite all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by changing pending to it.

Ginna Baker

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

bracket_push_spec.cr

require "spec"
require "../src/*"

describe "Brackets" do
describe "#are_valid?" do
it "paired square brackets" do
Brackets.are_valid?("[]").should be_true
end
it "empty string" do
Brackets.are_valid?("").should be_true
end
it "unpaired brackets" do
Brackets.are_valid?("[[").should be_false
end
it "wrong ordered brackets" do
Brackets.are_valid?("}{").should be_false
end
it "paired with whitespace" do
Brackets.are_valid?("{ }").should be_true
end
it "simple nested brackets" do
Brackets.are_valid?("{[]}").should be_true
end
it "several paired brackets" do
Brackets.are_valid?("{}[]").should be_true
end
it "paired and nested brackets" do
Brackets.are_valid?("([{}({}[])])").should be_true
end
it "unopened closing brackets" do
Brackets.are_valid?("{[)][]}").should be_false
end
it "unpaired and nested brackets" do
Brackets.are_valid?("([{])").should be_false
end
it "paired and wrong nested brackets" do
Brackets.are_valid?("[({]})").should be_false
end
it "math expression" do
Brackets.are_valid?("(((185 + 223.85) * 15) - 543)/2").should be_true
end
it "complex latex expression" do
Brackets.are_valid?("\left(\begin{array}{cc} \frac{1}{3} & x\\ \mathrm{e}^{x} &... x^2 \end{array}\right)").should be_true
end
end
end
module Brackets

PAIRS = {
']' => '[',
')' => '(',
'}' => '{'
}

def self.are_valid?(s : String) : Bool
a = [] of Char

s.each_char { |c|
pc = PAIRS[c]?

if PAIRS.values.includes?(c)
a.push(c)
elsif pc
if a.last? == nil || a.last != pc
return false
end
a.pop
end
}

a.empty?
end

end

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