Problem 22: generate parentheses

problems/22-generate-parentheses/main.rb

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+# Naive bruteforce solution
+
+# @param {Integer} n
+# @return {String[]}
+def generate_parenthesis(n)
+  combinations = ['(']
+
+  # Generate an array of all possible combinations
+  (2..n * 2).each do |i|
+    new_iteration = []
+
+    combinations.each do |elem|
+      new_iteration.push("#{elem})")
+      # Opening bracket can't be the last one
+      new_iteration.push("#{elem}(") if i != n * 2
+    end
+
+    combinations = new_iteration
+  end
+
+  # Return only valid combinations
+  combinations.select { |l| parenthesis_valid?(l) }
+end
+
+def parenthesis_valid?(s)
+  open_brackets = 0
+
+  s.each_char do |char|
+    if char == '('
+      open_brackets += 1
+    else
+      open_brackets -= 1
+    end
+    return false if open_brackets.negative?
+  end
+
+  return false if open_brackets.positive?
+
+  true
+end

problems/22-generate-parentheses/readme.md

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+# 22. Generate Parentheses
+
+Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
+
+- Example 1:
+
+```
+Input: n = 3
+Output: ["((()))","(()())","(())()","()(())","()()()"]
+```
+
+- Example 2:
+
+```
+Input: n = 1
+Output: ["()"]
+```
+
+## Constraints:
+
+```
+1 <= n <= 8
+```

problems/22-generate-parentheses/test.rb

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+require_relative 'main'
+require 'test/unit'
+
+class TestParenthesesGenerator < Test::Unit::TestCase
+  def test_one_level
+    res = generate_parenthesis(1)
+    assert_equal(['()'], res)
+  end
+
+  def test_three_levels
+    res = generate_parenthesis(3)
+    out = %w[((())) (()()) (())() ()(()) ()()()]
+
+    out.each do |p|
+      assert(res.include?(p), "Missing: #{p}")
+    end
+
+    assert_equal(out.count, res.count)
+  end
+
+  def test_five_levels
+    res = generate_parenthesis(5)
+    out = %w[((((())))) (((()()))) (((())())) (((()))()) (((())))() ((()(()))) ((()()())) ((()())()) ((()()))() ((())(())) ((())()()) ((())())() ((()))(()) ((()))()() (()((()))) (()(()())) (()(())()) (()(()))() (()()(())) (()()()()) (()()())() (()())(()) (()())()() (())((())) (())(()()) (())(())() (())()(()) (())()()() ()(((()))) ()((()())) ()((())()) ()((()))() ()(()(())) ()(()()()) ()(()())() ()(())(()) ()(())()() ()()((())) ()()(()()) ()()(())() ()()()(()) ()()()()()]
+
+    out.each do |p|
+      assert(res.include?(p), "Missing: #{p}")
+    end
+
+    assert_equal(out.count, res.count)
+  end
+end