balanced parentheses

Author: justcoding121

Advanced.Algorithms.Tests/Advanced.Algorithms.Tests.csproj

@@ -152,6 +152,7 @@
     <Compile Include="DataStructures\Tree\BinaryTree_Tests.cs" />
     <Compile Include="DynamicProgramming\Count\DigitCounter_Tests.cs" />
     <Compile Include="Geometry\PointRotation_Tests.cs" />
+    <Compile Include="Miscellaneous\BalanceParentheses_Tests.cs" />
     <Compile Include="Miscellaneous\CountInversions_Tests.cs" />
     <Compile Include="Miscellaneous\MatrixMultiplication_Tests.cs" />
     <Compile Include="DynamicProgramming\Maximizing\LongestChain_Tests.cs" />

Advanced.Algorithms.Tests/Miscellaneous/BalanceParentheses_Tests.cs

@@ -0,0 +1,34 @@
+using Advanced.Algorithms.Miscellaneous;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Advanced.Algorithms.Tests.Miscellaneous
+{
+    [TestClass]
+    public class BalanceParentheses_Tests
+    {
+        [TestMethod]
+        public void BalanceParentheses_Smoke_Test()
+        {
+            Assert.AreEqual("ab", BalanceParentheses.Balance("ab"));
+            Assert.AreEqual("ab", BalanceParentheses.Balance("((ab"));
+            Assert.AreEqual("ab", BalanceParentheses.Balance("(ab"));
+            Assert.AreEqual("ab", BalanceParentheses.Balance("ab))"));
+
+            Assert.AreEqual("((ab))", BalanceParentheses.Balance("((ab))"));
+            Assert.AreEqual("(ab)", BalanceParentheses.Balance("(ab))"));
+            Assert.AreEqual("(ab)", BalanceParentheses.Balance("((ab)"));
+
+            Assert.AreEqual("a(b)", BalanceParentheses.Balance("a(b)"));
+            Assert.AreEqual("", BalanceParentheses.Balance("(((("));
+            Assert.AreEqual("(()())", BalanceParentheses.Balance("(()())"));
+
+            Assert.AreEqual("ab()", BalanceParentheses.Balance(")ab(()"));
+            Assert.AreEqual("ab()", BalanceParentheses.Balance(")))ab(()(("));
+        }
+    }
+}

Advanced.Algorithms/Miscellaneous/BalanceParentheses.cs

@@ -0,0 +1,84 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Advanced.Algorithms.Miscellaneous
+{
+    public class BalanceParentheses
+    {
+        /// <summary>
+        /// O(n) time complexity
+        /// </summary>
+        /// <param name="text"></param>
+        /// <returns></returns>
+        public static string Balance(string text)
+        {
+            var result = new StringBuilder();
+
+            for (int i = 0; i < text.Length; i++)
+            {
+                var progress = Balance(text, i, result);
+
+                if (progress == i)
+                {
+                    continue;
+                }
+
+                i = progress;
+            }
+
+            return result.ToString();
+        }
+
+        /// <summary>
+        /// Recursively visit child parentheses and add balanced items to result
+        /// </summary>
+        /// <param name="text"></param>
+        /// <param name="i"></param>
+        /// <param name="result"></param>
+        /// <returns></returns>
+        public static int Balance(string text, int i, StringBuilder result)
+        {
+            if (i >= text.Length)
+            {
+                return text.Length;
+            }
+
+            //close parentheses
+            if (text[i] == ')')
+            {
+                return i;
+            }
+
+            //a character
+            if (text[i] != '(' && text[i] != ')')
+            {
+                result.Append(text[i]);
+                return Balance(text, i + 1, result);
+            }
+
+            //open parenthesis
+
+            var subResult = new StringBuilder();
+            while (i + 1 < text.Length && text[i] == '(')
+            {
+                i = Balance(text, i + 1, subResult);
+
+                if (i < text.Length && text[i] == ')')
+                {
+                    result.Append("(" + subResult.ToString() + ")");
+                }
+                else
+                {
+                    result.Append(subResult.ToString());
+                }
+
+                subResult.Clear();
+                i++;
+            }
+
+            return i;
+        }
+    }
+}

README.md

@@ -377,4 +377,6 @@ All are top down solutions with memoization technique.
 
 - [X] Count Inversions ([Implementation](https://github.com/justcoding121/Advanced-Algorithms/tree/develop/Advanced.Algorithms/Miscellaneous/CountInversions.cs) | [Tests](https://github.com/justcoding121/Advanced-Algorithms/tree/develop/Advanced.Algorithms.Tests/Miscellaneous/CountInversions_Tests.cs))
 - [X] Matrix Multiplication ([Implementation](https://github.com/justcoding121/Advanced-Algorithms/tree/develop/Advanced.Algorithms/Miscellaneous/MatrixMultiplication.cs) | [Tests](https://github.com/justcoding121/Advanced-Algorithms/tree/develop/Advanced.Algorithms.Tests/Miscellaneous/MatrixMultiplication_Tests.cs))
+- [X] Balanced Parentheses ([Implementation](https://github.com/justcoding121/Advanced-Algorithms/tree/develop/Advanced.Algorithms/Miscellaneous/BalanceParentheses.cs) | [Tests](https://github.com/justcoding121/Advanced-Algorithms/tree/develop/Advanced.Algorithms.Tests/Miscellaneous/BalanceParentheses_Tests.cs))
 
+