Create algorithm_quicksort.py (#141)

This file contains the program to perform quicksort along with explaination

Author: sadiah7

languages/python/algorithm_quicksort.py

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+# Quick sort in Python
+
+# The basic idea behind Quick Sort is to first find an element Pivot from the array
+# Based on pivot element, the array is sorted such that all the elements to the left of pivot are smaller
+# than pivot and elements to right of pivot are greater than pivot
+# The same process is repeated in the left and right sub array of the pivot.
+
+
+# function to find the partition position
+def partition(array, low, high):
+
+    # choose the rightmost element as pivot
+    pivot = array[high]
+
+    # pointer for greater element
+    i = low - 1
+
+    # traverse through all elements
+    # compare each element with pivot
+    for j in range(low, high):
+        if array[j] <= pivot:
+            # if element smaller than pivot is found
+            # swap it with the greater element pointed by i
+            i = i + 1
+
+            # swapping element at i with element at j
+            (array[i], array[j]) = (array[j], array[i])
+
+    # swap the pivot element with the greater element specified by i
+    (array[i + 1], array[high]) = (array[high], array[i + 1])
+
+    # return the position from where partition is done
+    return i + 1
+
+def quickSort(array, low, high):
+    if low < high:
+
+        # find pivot element such that
+        # element smaller than pivot are on the left
+        # element greater than pivot are on the right
+        pi = partition(array, low, high)
+
+        # recursive call on the left of pivot
+        quickSort(array, low, pi - 1)
+
+        # recursive call on the right of pivot
+        quickSort(array, pi + 1, high)
+
+
+data = [10, 11, 3, 5, 16, 34, 15]
+print("Unsorted Array")
+print(data)
+
+size = len(data)
+
+quickSort(data, 0, size - 1)
+
+print('Sorted Array in Ascending Order:')
+print(data)