Algorithms and Data Structures in C#: A Practical Guide with Examples

Algorithms and Data Structures in C#: In Practice

Understanding algorithms and data structures is a fundamental skill for any developer. Whether you are writing a high-load service, a desktop application, or a game, efficient data management directly impacts the performance and scalability of your code. In this article, we will break down key data structures and algorithms in C# (.NET) with practical examples that you can immediately apply in your projects.

1. Dynamic Arrays and Working with List<T>

In C#, the basic dynamic array is the List<T> class. Unlike a classic array, it automatically expands when elements are added. Let's look at its key operations and one of the most important ones — binary search.

Binary Search only works on sorted data. Its complexity is O(log n). The algorithm halves the search range at each step.

using System;\nusing System.Collections.Generic;\n\npublic class BinarySearchExample\n{\n    public static int BinarySearch(List<int> sortedList, int target)\n    {\n        int left = 0;\n        int right = sortedList.Count - 1;\n\n        while (left <= right)\n        {\n            int mid = left + (right - left) / 2;\n\n            if (sortedList[mid] == target)\n                return mid; // Element found, return index\n            else if (sortedList[mid] < target)\n                left = mid + 1; // Search in the right half\n            else\n                right = mid - 1; // Search in the left half\n        }\n        return -1; // Element not found\n    }\n\n    public static void Main()\n    {\n        var numbers = new List<int> { 2, 5, 8, 12, 16, 23, 38, 45, 56, 67 };\n        int target = 23;\n        int result = BinarySearch(numbers, target);\n        Console.WriteLine(result != -1 ? $"Element {target} found at index {result}" : "Element not found");\n    }\n}

Why is this important? List<T> is used in 90% of projects. The ability to quickly search data in it is key to performance.

2. Stack and Queue: LIFO and FIFO in Practice

Stack and Queue are collections with a clearly defined access order. They are indispensable for processing calls, syntactic analysis, and working with tasks.

Stack (LIFO — Last In, First Out)

It is used, for example, to check the correctness of brackets in code.

using System;\nusing System.Collections.Generic;\n\npublic class StackExample\n{\n    public static bool IsValidBrackets(string input)\n    {\n        Stack<char> stack = new Stack<char>();\n        foreach (char ch in input)\n        {\n            if (ch == '(' || ch == '{' || ch == '[')\n            {\n                stack.Push(ch);\n            }\n            else if (ch == ')' || ch == '}' || ch == ']')\n            {\n                if (stack.Count == 0) return false;\n\n                char top = stack.Pop();\n                if ((ch == ')' && top != '(') ||\n                    (ch == '}' && top != '{') ||\n                    (ch == ']' && top != '['))\n                {\n                    return false;\n                }\n            }\n        }\n        return stack.Count == 0;\n    }\n\n    public static void Main()\n    {\n        string test1 = "({[]})";\n        string test2 = "({[})";\n        Console.WriteLine($"'{test1}' — correct brackets: {IsValidBrackets(test1)}");\n        Console.WriteLine($"'{test2}' — correct brackets: {IsValidBrackets(test2)}");\n    }\n}

Queue (FIFO — First In, First Out)

Perfectly suited for processing tasks in the order they arrive (e.g., a print queue).

using System;\nusing System.Collections.Generic;\n\npublic class QueueExample\n{\n    public static void Main()\n    {\n