Example: Quick Sort Implementation in C++

// Quick Sort Implementation
#include <iostream>
#include <vector>
#include <algorithm> // For std::swap

// Function to partition the array
// It takes the last element as pivot, places the pivot element at its correct position
// in sorted array, and places all smaller (than pivot) to left of pivot
// and all greater elements to right of pivot.
int partition(std::vector<int>& arr, int low, int high) {
    int pivot = arr[high]; // Choosing the last element as pivot
    int i = (low - 1);     // Index of smaller element

    for (int j = low; j <= high - 1; j++) {
        // If current element is smaller than or equal to pivot
        if (arr[j] <= pivot) {
            i++; // Increment index of smaller element
            std::swap(arr[i], arr[j]);
        }
    }
    std::swap(arr[i + 1], arr[high]);
    return (i + 1);
}

// The main function that implements QuickSort
// arr[] --> Array to be sorted,
// low --> Starting index,
// high --> Ending index
void quickSort(std::vector<int>& arr, int low, int high) {
    if (low < high) {
        // pi is partitioning index, arr[pi] is now at right place
        int pi = partition(arr, low, high);

        // Separately sort elements before partition and after partition
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}

// Function to print an array
void printArray(const std::vector<int>& arr) {
    for (int x : arr) {
        std::cout << x << " ";
    }
    std::cout << std::endl;
}

int main() {
    // Step 1: Initialize an unsorted array
    std::vector<int> arr = {10, 7, 8, 9, 1, 5};
    int n = arr.size();

    std::cout << "Original array: ";
    printArray(arr);

    // Step 2: Apply Quick Sort
    quickSort(arr, 0, n - 1);

    std::cout << "Sorted array: ";
    printArray(arr);

    // Another example
    std::vector<int> arr2 = {2, 8, 7, 1, 3, 5, 6, 4};
    n = arr2.size();

    std::cout << "\nOriginal array 2: ";
    printArray(arr2);

    quickSort(arr2, 0, n - 1);

    std::cout << "Sorted array 2: ";
    printArray(arr2);

    return 0;
}