Example: Quick Sort in C++ in C++

// Quick Sort in C++
#include <iostream>
#include <vector> // Using std::vector for dynamic array
#include <algorithm> // For std::swap

// Function to swap two elements
void swap(int* a, int* b) {
    int t = *a;
    *a = *b;
    *b = t;
}

/* This function takes 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]; // Pivot is the last element
    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
            swap(&arr[i], &arr[j]);
        }
    }
    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 i = 0; i < arr.size(); i++) {
        std::cout << arr[i] << " ";
    }
    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();

    // Step 2: Print the original array
    std::cout << "Original array: ";
    printArray(arr);

    // Step 3: Apply Quick Sort
    quickSort(arr, 0, n - 1);

    // Step 4: Print the sorted array
    std::cout << "Sorted array: ";
    printArray(arr);

    return 0;
}