QuickSort.java

// Java implementation of QuickSort
import java.io.*;

class QuickSort {

    // A utility function to swap two elements
    static void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }

    /*
     * This function takes last element as pivot, places
     * the pivot element at its correct position in sorted
     * array, and places all smaller (smaller than pivot)
     * to left of pivot and all greater elements to right
     * of pivot
     */
    static int partition(int[] arr, int low, int high) {

        // pivot
        int pivot = arr[high];

        // Index of smaller element and
        // indicates the right position
        // of pivot found so far
        int i = (low - 1);

        for (int j = low; j <= high - 1; j++) {

            // If current element is smaller
            // than the pivot
            if (arr[j] < pivot) {

                // Increment index of
                // smaller element
                i++;
                swap(arr, i, j);
            }
        }
        swap(arr, i + 1, high);
        return (i + 1);
    }

    /*
     * The main function that implements QuickSort
     * arr[] --> Array to be sorted,
     * low --> Starting index,
     * high --> Ending index
     */
    static void quickSort(int[] arr, int low, int high) {
        if (low < high) {

            // pi is partitioning index, arr[p]
            // 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
    static void printArray(int[] arr, int size) {
        for (int i = 0; i < size; i++)
            System.out.print(arr[i] + " ");

        System.out.println();
    }

    // Driver Code
    public static void main(String[] args) {
        int[] arr = { 10, 7, 8, 9, 1, 5 };
        int n = arr.length;

        quickSort(arr, 0, n - 1);
        System.out.println("Sorted array: ");
        printArray(arr, n);
    }
}

// This code is contributed by Ayush Choudhary