# Quick Sort

Nishant Kumar
·Feb 1, 2022·

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Quick Sort is an algorithm for sorting which is based on divide and conquer approach. An element is chosen as pivot and partitions the given list. The elements are swapped, based on comparison with pivot value, in order to obtain a sorted list. The partitioned sub lists are recursively called to sort the elements in list. The selection of pivot can decide the efficiency of the quick sort.

### Illustration:

``````partition(list,lowestIndex,highestIndex)
pointerI=lowestIndex-1
pivot=Element at highestIndex
for pointerJ from lowestIndex to HighestIndex
if ElementAtpointerJ < pivot
pointerI=pointerI+1
swap ElementAtpointerI with ElementAtpointerJ
swap Element at pointerI+1 with pivot
return i+1

quickSort(list,lowestIndex,highestIndex)
if lowestIndex < highestIndex
pivotIndex=partition(list,lowestIndex,highestIndex)
recursiveCall on left part, quickSort(list,lowestIndex,pivotIndex-1)
recursiveCall on right part, quickSort(list,pivotIndex+1,highestIndex)
``````

Time Complexity:

• Worst Case: O(n2)
• Average Case: O(nlogn)
• Best Case: O(nlogn) Space Complexity: O(logn)

### Program for Quick Sort:

``````def partition(data,low,high):
i = ( low-1 )         # Index of smaller element
pivot = data[high]     # Pivot Value

for j in range(low , high):

if   data[j] < pivot:         # If current element is smaller than the pivot

i = i+1             # Increment index of smaller element
data[i],data[j] = data[j],data[i]
data[i+1],data[high] = data[high],data[i+1]
return ( i+1 )

def quickSort(data, low, high):
if low < high:

# Select pivot position and put all the elements smaller than pivot on left and greater than pivot on right
pi = partition(data, low, high)

# Sort the elements on the left of pivot
quickSort(data, low, pi - 1)

# Sort the elements on the right of pivot
quickSort(data, pi + 1, high)

inp=input("Enter the data: ").split()
data=[]
for i in inp:
data.append(int(i))
quickSort(data, 0, len(data) - 1)
print('Sorted list in Ascending Order:')
print(data)
``````