C++ algorithm Library

Welcome to The Coding College! This tutorial explores the C++ <algorithm> library, a powerful collection of functions for performing common operations on containers such as arrays, vectors, lists, and other Standard Template Library (STL) data structures.

What is the <algorithm> Library?

The <algorithm> library provides functions for:

  • Sorting: Arrange elements in ascending/descending order.
  • Searching: Find specific elements or ranges.
  • Modifying: Transform or reorder elements.
  • Utility Operations: Perform computations like minimum, maximum, and comparisons.

To use these functions, include the library in your program:

#include <algorithm>

Key Features of <algorithm>

  1. Versatile: Works seamlessly with STL containers.
  2. Generic: Uses iterators, making it compatible with various data structures.
  3. Performance Optimized: Provides efficient implementations of common algorithms.

Commonly Used <algorithm> Functions

1. Sorting Functions

FunctionDescription
sort()Sorts a range in ascending order.
stable_sort()Maintains the relative order of equal elements.
partial_sort()Sorts the first few elements.

2. Searching Functions

FunctionDescription
binary_search()Checks if an element exists (sorted containers).
find()Finds an element in a range.

3. Utility Functions

FunctionDescription
min()Returns the smaller of two elements.
max()Returns the larger of two elements.
swap()Swaps the values of two elements.

4. Modification Functions

FunctionDescription
reverse()Reverses the order of elements in a range.
transform()Applies a function to each element.
remove()Removes specific values from a range.

Example: Sorting a Vector

Here’s how to sort a vector of integers using the <algorithm> library:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    vector<int> numbers = {50, 20, 40, 10, 30};

    // Sort in ascending order
    sort(numbers.begin(), numbers.end());

    cout << "Sorted numbers: ";
    for (int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Output:

Sorted numbers: 10 20 30 40 50

Example: Binary Search

Check if an element exists in a sorted range:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    vector<int> numbers = {10, 20, 30, 40, 50};

    // Check for existence of an element
    bool found = binary_search(numbers.begin(), numbers.end(), 30);

    if (found) {
        cout << "30 is in the list." << endl;
    } else {
        cout << "30 is not in the list." << endl;
    }

    return 0;
}

Output:

30 is in the list.

Example: Reverse a Range

Reverse the order of elements in a container:

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    vector<int> numbers = {10, 20, 30, 40, 50};

    // Reverse the vector
    reverse(numbers.begin(), numbers.end());

    cout << "Reversed numbers: ";
    for (int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Output:

Reversed numbers: 50 40 30 20 10

Example: Find the Maximum and Minimum

#include <iostream>
#include <algorithm>
using namespace std;

int main() {
    int a = 10, b = 20;

    cout << "Maximum: " << max(a, b) << endl;
    cout << "Minimum: " << min(a, b) << endl;

    return 0;
}

Output:

Maximum: 20
Minimum: 10

Using Custom Comparators

You can pass custom comparison functions to certain algorithms.

Example: Sort in Descending Order

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

bool descending(int a, int b) {
    return a > b;
}

int main() {
    vector<int> numbers = {10, 20, 30, 40, 50};

    // Sort in descending order
    sort(numbers.begin(), numbers.end(), descending);

    cout << "Descending order: ";
    for (int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Output:

Descending order: 50 40 30 20 10

Real-Life Example: Removing Duplicates

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    vector<int> numbers = {10, 20, 10, 30, 20, 40, 50};

    // Remove duplicates
    sort(numbers.begin(), numbers.end());
    auto it = unique(numbers.begin(), numbers.end());
    numbers.erase(it, numbers.end());

    cout << "Unique elements: ";
    for (int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Output:

Unique elements: 10 20 30 40 50

Summary

The <algorithm> library is a cornerstone of modern C++ programming, providing efficient and reusable implementations of common operations. Whether you need to sort, search, modify, or transform data, this library has you covered.

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