feat: Add parentheses example.

README.md

@@ -16,6 +16,7 @@ So far, the following exercises have been covered:
 - [Floyd](./floyd/) – implements Floyd's cycle-finding "Tortoise and Hare" algorithm
 - [Heap](./heap/) – implements a heap from scratch, without using the built-in `container/heap` package
 - [Markov count](./markovcount/) – figures out how often states are reached by a Markov chain
+- [Parentheses](./parentheses/) – checks if a string has balanced parentheses.
 - [Radix sort](./radixsort/) – implements radix sort
 - [Remove k-th last element](./removekthlastelement/) – removes the k-th last element from a single-linked list
 - [Run-length encoding](./runlengthencoding/) – encodes and decodes strings using run-length encoding

parentheses/documentation.go

@@ -0,0 +1,2 @@
+// Package parentheses checks if a string has balanced parentheses.
+package parentheses

parentheses/is_balanced.go

@@ -0,0 +1,24 @@
+package parentheses
+
+func IsBalanced(s string) bool {
+	low, high := 0, 0
+	for _, char := range s {
+		switch char {
+		case '(':
+			low++
+			high++
+		case ')':
+			low = max(low-1, 0)
+			high--
+		case '*':
+			low = max(low-1, 0)
+			high++
+		}
+
+		if high < 0 {
+			return false
+		}
+	}
+
+	return low == 0
+}

parentheses/is_balanced_test.go

@@ -0,0 +1,48 @@
+package parentheses_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/thenativeweb/codingcircle/parentheses"
+)
+
+func TestIsBalanced(t *testing.T) {
+	t.Run("empty string", func(t *testing.T) {
+		assert.True(t, parentheses.IsBalanced(""))
+	})
+
+	t.Run("balanced string", func(t *testing.T) {
+		assert.True(t, parentheses.IsBalanced("()"))
+		assert.True(t, parentheses.IsBalanced("(())"))
+		assert.True(t, parentheses.IsBalanced("()()"))
+		assert.True(t, parentheses.IsBalanced("(()())"))
+		assert.True(t, parentheses.IsBalanced("((()))"))
+	})
+
+	t.Run("unbalanced string", func(t *testing.T) {
+		assert.False(t, parentheses.IsBalanced("("))
+		assert.False(t, parentheses.IsBalanced(")"))
+		assert.False(t, parentheses.IsBalanced(")("))
+		assert.False(t, parentheses.IsBalanced("())"))
+		assert.False(t, parentheses.IsBalanced("(()"))
+		assert.False(t, parentheses.IsBalanced("((())"))
+	})
+
+	t.Run("balanced string with wildcard", func(t *testing.T) {
+		assert.True(t, parentheses.IsBalanced("*"))
+		assert.True(t, parentheses.IsBalanced("(*)"))
+		assert.True(t, parentheses.IsBalanced("(*))"))
+		assert.True(t, parentheses.IsBalanced("(**))*"))
+		assert.True(t, parentheses.IsBalanced("*((**))*"))
+		assert.True(t, parentheses.IsBalanced("(***"))
+	})
+
+	t.Run("unbalanced string with wildcard", func(t *testing.T) {
+		assert.False(t, parentheses.IsBalanced("*("))
+		assert.False(t, parentheses.IsBalanced("*)("))
+		assert.False(t, parentheses.IsBalanced("***("))
+		assert.False(t, parentheses.IsBalanced("(***(()"))
+		assert.False(t, parentheses.IsBalanced("(**("))
+	})
+}