How do I implement Quicksort in C++?

How do I implement Quicksort in C++?

To implement Quicksort in C++, you can follow these steps: 1. Choose a pivot element. 2. Partition the array. 3. Recursively sort the sub-arrays.

Can you show me a sample code for that?

Sure! Here's a simple implementation:

#include <iostream>
using namespace std;

int partition(int arr[], int low, int high) {
    int pivot = arr[high];
    int i = (low - 1);
    for (int j = low; j < high; j++) {
        if (arr[j] < pivot) {
            i++;
            swap(arr[i], arr[j]);
        }
    }
    swap(arr[i + 1], arr[high]);
    return (i + 1);
}

void quickSort(int arr[], int low, int high) {
    if (low < high) {
        int pi = partition(arr, low, high);
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}

int main() {
    int arr[] = {10, 7, 8, 9, 1, 5};
    int n = sizeof(arr) / sizeof(arr[0]);
    quickSort(arr, 0, n - 1);
    cout << "Sorted array: ";
    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";
    return 0;
}

This code sorts an array using the Quicksort algorithm.

What is the time complexity of Quicksort?

The average time complexity of Quicksort is O(n log n), while the worst-case time complexity is O(n²), which occurs when the smallest or largest element is always chosen as the pivot.