Algorithms and Data Structures in C++: A Complete Guide for Beginners

Algorithms and Data Structures in C++: From Basics to Practice

Mastering algorithms and data structures is a key stage in the development of any programmer. In this article, we will break down fundamental concepts using the C++ language as an example. You will learn how to efficiently organize data and write fast algorithms that will form the foundation of your projects. The material is designed for beginners and intermediate developers.

What are Algorithms and Data Structures?

An algorithm is a clear sequence of actions for solving a problem. A data structure is a way of organizing and storing data, ensuring efficient access and modification. In C++, both concepts are closely related: choosing the right data structure can speed up an algorithm by tens of times.

Basic data structures in C++:

• Arrays — a fixed set of elements of the same type
• Linked lists — dynamic sequences
• Stacks and queues — structures with restricted access
• Trees — hierarchical structures
• Hash tables — fast key-based search

Arrays and Working with Them

An array is the simplest data structure, where elements are stored in a contiguous memory area. In C++, arrays can be static and dynamic.

#include <iostream>using namespace std;

int main() {    // Static array    int arr[5] = {10, 20, 30, 40, 50};        // Dynamic array (via new)    int* dynArr = new int[3];    dynArr[0] = 1;    dynArr[1] = 2;    dynArr[2] = 3;        // Output elements    for (int i = 0; i < 5; i++) {        cout << arr[i] << " ";    }        delete[] dynArr; // Free memory    return 0;}

Linear search algorithm in an array:

int linearSearch(int arr[], int n, int x) {    for (int i = 0; i < n; i++) {        if (arr[i] == x)            return i; // Return index    }    return -1; // Not found}

Complexity: O(n). To speed things up, use std::vector from the STL — it manages memory automatically.

Linked Lists: Singly Linked and Doubly Linked

A linked list consists of nodes, each containing data and a pointer to the next (or previous) element. In C++, std::forward_list (singly linked) and std::list (doubly linked) are often used.

Implementation of a simple singly linked list:

struct Node {    int data;    Node* next;};

class LinkedList {private:    Node* head;public:    LinkedList() : head(nullptr) {}        void insert(int val) {        Node* newNode = new Node{val, nullptr};        if (!head) {            head = newNode;            return;        }        Node* temp = head;        while (temp->next) temp = temp->next;        temp->next = newNode;    }        void display() {        Node* temp = head;        while (temp) {            cout << temp->data << " -> ";            temp = temp->next;        }        cout << "nullptr" << endl;    }};

Advantages of lists:

• Dynamic size
• Fast insertion and deletion in the middle (O(1) if you have a pointer)

Disadvantages:

• Slow access by index (O(n))
• Additional memory for pointers

Stack and Queue: LIFO and FIFO Principles

A stack works on the "last in, first out" (LIFO) principle. A queue works on the "first in, first out" (FIFO) principle. In C++, they are implemented in the STL.

Example of using a stack:

#include <stack>#include