# Code - Quick Sort

## Quick sort in python

# Python program for implementation of Quicksort Sort

# 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
def partition(arr,low,high):
i = ( low-1 )         # index of smaller element
pivot = arr[high]     # pivot

for j in range(low , high):

# If current element is smaller than or
# equal to pivot
if   arr[j] <= pivot:

# increment index of smaller element
i = i+1
arr[i],arr[j] = arr[j],arr[i]

arr[i+1],arr[high] = arr[high],arr[i+1]
return ( i+1 )

# The main function that implements QuickSort
# arr[] --> Array to be sorted,
# low  --> Starting index,
# high  --> Ending index

# Function to do Quick sort
def quickSort(arr,low,high):
if low < high:

# pi is partitioning index, arr[p] is now
# at right place
pi = partition(arr,low,high)

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

# Driver code to test above
arr = [10, 7, 8, 9, 1, 5]
n = len(arr)
quickSort(arr,0,n-1)
print ("Sorted array is:")
for i in range(n):
print ("%d" %arr[i]),

# This code is contributed by Mohit Kumra


quicksort :: ( Ord a ) = > [ a ] -> [ a ]
quicksort [] = []
quicksort ( x : xs ) =
let smallerSorted = quicksort [ a | a <- xs , a <= x ]
biggerSorted = quicksort [ a | a <- xs , a > x ]
in smallerSorted ++ [ x ] ++ biggerSorted


## Quick sort in scheme

(define (quicksort lst)
(cond
((or (null? lst) ; empty list is sorted
(null? (cdr lst))) ; single-element list is sorted
lst)
(else
(let ((pivot (car lst)) ; Select the first element as the pivot
(rest (cdr lst)))
(append
(quicksort ; Recursively sort the list of smaller values
(filter (lambda (x) (< x pivot)) rest)) ; Select the smaller values
(list pivot) ; Add the pivot in the middle
(quicksort ; Recursively sort the list of larger values
(filter (lambda (x) (>= x pivot)) rest))))))) ; Select the larger and equal values


## Quick sort in java

package com.theme.rouge;

public class MyQuickSort {

private int array[];
private int length;

public void sort(int[] inputArr) {

if (inputArr == null || inputArr.length == 0) {
return;
}
this.array = inputArr;
length = inputArr.length;
quickSort(0, length - 1);
}

private void quickSort(int lowerIndex, int higherIndex) {

int i = lowerIndex;
int j = higherIndex;
// calculate pivot number, I am taking pivot as middle index number
int pivot = array[lowerIndex+(higherIndex-lowerIndex)/2];
// Divide into two arrays
while (i <= j) {
/**
* In each iteration, we will identify a number from left side which
* is greater then the pivot value, and also we will identify a number
* from right side which is less then the pivot value. Once the search
* is done, then we exchange both numbers.
*/
while (array[i] < pivot) {
i++;
}
while (array[j] > pivot) {
j--;
}
if (i <= j) {
exchangeNumbers(i, j);
//move index to next position on both sides
i++;
j--;
}
}
// call quickSort() method recursively
if (lowerIndex < j)
quickSort(lowerIndex, j);
if (i < higherIndex)
quickSort(i, higherIndex);
}

private void exchangeNumbers(int i, int j) {
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}

public static void main(String a[]){

MyQuickSort sorter = new MyQuickSort();
int[] input = {24,2,45,20,56,75,2,56,99,53,12};
sorter.sort(input);
for(int i:input){
System.out.print(i);
System.out.print(" ");
}
}
}