C#: Verify that a string contains valid parentheses

Last update on June 24 2025 12:58:09 (UTC/GMT +8 hours)

Validate Brackets in String

A given string contains the bracket characters '(', ')', '{', '}', '<', ‘>', '[' and ']',
Write a C# programme to check the said string is valid or not. The input string will be valid when open brackets and closed brackets are same type of brackets.
Or
open brackets will be closed in proper order.

Sample Data:
( "<>") -> True
("<>()[]{}") -> True
("(<>") -> False
("[<>()[]{}]") -> True

Sample Solution-1:

C# Sharp Code:

using System;
using System.Collections.Generic;

namespace exercises
{
    class Program
    {
        static void Main(string[] args)
        {
            // Initializing different strings containing various parentheses combinations
            string text = "<>";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));

            text = "<>()[]{}";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));

            text = "(<>";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));

            text = "[<>()[]{}]";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));
        }

        // Method to verify if a string contains valid parentheses
        public static bool test(string s)
        {
            // Creating a stack to store opening parentheses
            Stack<char> ch = new Stack<char>();

            // Iterating through each character in the input string
            foreach (var item in s.ToCharArray())
            {
                // Checking the type of parentheses and pushing the respective closing parentheses onto the stack
                if (item == '(')
                    ch.Push(')');
                else if (item == '<')
                    ch.Push('>');
                else if (item == '[')
                    ch.Push(']');
                else if (item == '{')
                    ch.Push('}');
                else if (ch.Count == 0 || ch.Pop() != item)
                    return false; // If the closing parentheses don't match the top of the stack or stack is empty, return false
            }

            // If the stack is empty after processing all characters, return true, otherwise return false
            return ch.Count == 0;
        }
    }
}

Sample Output:

Original string: <>
Verify the said string contains valid parentheses: True
Original string: <>()[]{}
Verify the said string contains valid parentheses: True
Original string: (<>
Verify the said string contains valid parentheses: False
Original string: [<>()[]{}]
Verify the said string contains valid parentheses: True

Flowchart:

Sample Solution-2:

C# Sharp Code:

using System;

namespace exercises
{
    class Program
    {
        static void Main(string[] args)
        {
            // Initializing different strings containing various parentheses combinations
            string text = "<>";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));

            text = "<>()[]{}";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));

            text = "(<>";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));

            text = "[<>()[]{}]";
            Console.WriteLine("Original string: " + text);
            Console.WriteLine("Verify the said string contains valid parentheses: " + test(text));
        }

        // Method to verify if a string contains valid parentheses
        public static bool test(string text)
        {
            string temp_text = string.Empty;

            // Loop continues until the text doesn't change anymore after replacements
            while (text != temp_text)
            {
                temp_text = text;

                // Replacing pairs of parentheses with an empty string in each iteration
                text = text.Replace("<>", "").Replace("()", "").Replace("[]", "").Replace("{}", "");
            }

            // If the final text is empty, all parentheses are balanced, return true; otherwise, return false
            return text == string.Empty ? true : false;
        }
    }
}

Sample Output:

Original string: <>
Verify the said string contains valid parentheses: True
Original string: <>()[]{}
Verify the said string contains valid parentheses: True
Original string: (<>
Verify the said string contains valid parentheses: False
Original string: [<>()[]{}]
Verify the said string contains valid parentheses: True

Flowchart:

For more Practice: Solve these Related Problems:

Write a C# program to validate strings with multiple types of brackets including angle and curly braces.
Write a C# program to check if a string has balanced brackets using a custom stack implementation.
Write a C# program to count the number of properly matched bracket pairs in a given string.
Write a C# program to return the length of the longest valid bracket sequence in a string.

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