From 9640f596c6f5b146ae14b6198e15f74c421b77c0 Mon Sep 17 00:00:00 2001
From: "U-GT780R-W7HP\\stephen" <stephen@GT780R-W7HP.(none)>
Date: Fri, 7 Oct 2011 17:18:46 -0400
Subject: [PATCH] In-place quicksort in Python

---
 QuickSort.py | 85 ++++++++++++++++++++++++++++++++++++++++++----------
 README       |  2 +-
 2 files changed, 70 insertions(+), 17 deletions(-)

diff --git a/QuickSort.py b/QuickSort.py
index e86f812..37a8556 100755
--- a/QuickSort.py
+++ b/QuickSort.py
@@ -1,27 +1,80 @@
 import random
+import unittest
 
 def quicksort(array):
-    if len(array) < 2:
-        return array
+    def swap(a, b):
+        temp = array[a]
+        array[a] = array[b]
+        array[b] = temp
+        
+    def partition(array, begin, end):
+        # pick pivot elem and move to end
+        pivotIndex = random.randint(begin, end)
+        pivotElem = array[pivotIndex]
+        swap(pivotIndex, end)
+        
+        swapindex = begin
+        for i in xrange(begin, end):
+            if array[i] < pivotElem:
+                swap(swapindex, i)
+                swapindex += 1
+            
+        swap(swapindex, end)
+        return swapindex
     
-    # select a random pivot
-    pivot = array[random.randint(0, len(array) - 1)]
-    array.remove(pivot)
-    
-    less = []
-    greater = []
+    def doquicksort(array, begin, end):
+        arraylen = end-begin+1
+        
+        if arraylen < 2:
+            return
+        
+        pivotIndex = partition(array, begin, end)
+        
+        doquicksort(array, begin, pivotIndex-1)
+        doquicksort(array, pivotIndex+1, end)
+
+    doquicksort(array, 0, len(array)-1)
     
-    for elem in array:
-        if elem < pivot:
-            less.append(elem)
-        else:
-            greater.append(elem)
+class QuickSortTestFunctions(unittest.TestCase):
+
+    def isSorted(self, array):
+        if len(array) < 2:
+            return True
+        
+        prev_index = 0
+        
+        for i in xrange(1, len(array)):
+            if array[prev_index] > array[i]:
+                return False
+            prev_index = i
+            
+        return True
+
+    def sort_and_test(self, array):
+        quicksort(array)
+        return self.isSorted(array)
     
-    return quicksort(less) + [pivot] + quicksort(greater)
+    def test_sorted_empty(self):
+        self.assertTrue(self.sort_and_test([]))
+
+    def test_sorted_one(self):
+        self.assertTrue(self.sort_and_test([1]))
+
+    def test_sorted_two(self):
+        self.assertTrue(self.sort_and_test([2,1]))
+        self.assertTrue(self.sort_and_test([1,1]))
+        
+    def test_random(self):
+        for i in xrange(0, 100):
+            array = [ random.randint(-1000000, 1000000) for j in xrange(0, random.randint(20,100))]
+            self.assertTrue(self.sort_and_test(array))
 
 if __name__ == "__main__":
     
-    array = [ random.randint(0, 100) for i in range(0, 10) ]
+    array = [ random.randint(0, 100) for i in xrange(0, 20) ]
     
     print("Initial array is:", array)
-    print("Quicksorted array is:", quicksort(array))
+    quicksort(array)
+    print("Quicksorted array is:", array)
+
+    unittest.main()
\ No newline at end of file
diff --git a/README b/README
index c197a0d..68ba153 100644
--- a/README
+++ b/README
@@ -1,4 +1,4 @@
 Quicksort in Python
 
-Naive implementation using O(n) memory
+In-place implementation