Quick Sort

Hoare_quicksort.py

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+from random import randint
+def partition(arr, p ,r):
+    pivot = arr[p]
+    i = p - 1
+    j = r + 1
+    while True:
+        j -= 1
+        while j >= p and arr[j] > pivot :
+            j -= 1
+        i += 1
+        while i <= r  and arr[i] < pivot:
+            i += 1
+        if i < j:
+            arr[i], arr[j] = arr[j], arr[i]
+        else:
+            #arr[p], arr[j] = arr[j], arr[p] don't need to do this since we are calling quicksort [p,q] & (q,r]...
+            return j
+
+def quicksort(arr, p ,r):
+    if p < r:
+        q = partition(arr, p, r)
+        quicksort(arr, p, q)
+        quicksort(arr, q + 1, r)
+
+def main():
+    arr = [randint(-1,10) for i in range(9)]
+    print arr
+    print "applying Hoare's partition Quick Sort..."
+    quicksort(arr,0,len(arr) - 1)
+    print arr
+
+if __name__ == "__main__":
+    main()

K_th_smallest_quickSelect.py

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+from random import randint
+from time import time
+
+def partition(arr,p,r):
+    pivot = arr[r]
+    i = p - 1
+    for j in range(p,r):#using Lomuto's partition method...
+        if arr[j] <= pivot:
+            i += 1
+            arr[i],arr[j] =arr[j],arr[i]
+    arr[i + 1],arr[r] = arr[r],arr[i + 1]
+    return i + 1
+
+def quickselect(arr,p,r,key):
+    if p < r:
+        q = partition(arr,p,r)
+        if q  == key: # If partition index is equal to kth number stop...
+            return
+        elif q > key - 1: 
+            quickselect(arr,p,q-1,key)
+        else:
+            quickselect(arr,q+1,r,key)
+
+def main():
+    arr = [randint(-1,1000000) for i in range(1000000)]#picking numbers randomly 
+    print "Which smallest number you want to you wnat to find an above array?"
+    k = int(raw_input())
+    if k > len(arr):# k should be less than the length of input...
+        start = time()
+        raise "Invalid input: Exceeds the array limit ERROR."
+    else:
+        start = time()#calculate the time to find kth smallest
+        print "finding %dth smallest element..." % k
+        quickselect(arr,0,len(arr)-1,k-1)
+        #print arr
+        print arr[k-1]
+    print time() - start
+
+if __name__ == "__main__":#execution will start from here...
+    main()

quick_sort.py

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+from random import randint
+from time import time
+
+def partition(arr, p, r):
+    pivot = arr[r]
+    i = p - 1
+    for j in range(p, r):
+        if arr[j] <= pivot:
+            i += 1
+            arr[j], arr[i] = arr[i], arr[j]
+    else:
+        arr[i + 1],arr[r] = arr[r], arr[i + 1]
+    print "pivot = %d" % (i + 1)
+    print arr
+    return i + 1
+
+def quicksort(arr, p ,r):
+    if p < r:
+        q = partition(arr, p, r)
+        quicksort(arr, p, q - 1)
+        quicksort(arr, q + 1, r)
+
+def main():
+    arr = [randint(-1,10) for i in range(10)]
+    print arr
+    print "Applying quick sort..."
+    start = time()
+    quicksort(arr, 0, len(arr)- 1)
+    print time() - start
+
+if __name__ == "__main__":
+    main()

tail_recursion_QuickSort.py

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+from random import randint
+from time import time
+
+
+def partition(arr, p, r):
+	pivot = arr[p]
+	i = p - 1
+	j = r + 1
+	while True:
+		j -= 1
+		while j >= p and arr[j] > pivot:
+			j -= 1
+		i += 1
+		while i <= r and arr[i] < pivot:
+			i += 1
+		if i < j:
+			arr[i], arr[j] = arr[j], arr[i]
+		else:
+			return j
+
+def tail_recursion_quick_sort(arr, p, r):
+	while p < r:
+		q = partition(arr, p, r)
+		tail_recursion_quick_sort(arr, p, q)
+		p = q + 1
+
+def main():
+	arr = [randint(-1,11) for i in range(9)]
+	print arr
+	start = time()
+	print "Performing Tail Recursion Quick Sort..."
+	tail_recursion_quick_sort(arr,0,len(arr) - 1)
+	print arr
+	print time() - start
+
+if __name__ == "__main__":
+	main()
+