Add quick sort

.gitignore

@@ -0,0 +1,2 @@
+.cache
+__pycache__

arrays-and-strings/quick-sort.py

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+# Quick sort
+# The idea is to pick a pivot point and sort the array such that
+# the left part of the coverging point is smaller than the pivor point,
+# the right larger.
+# converging point is found when the right pointer is smaller than the left pointer
+import pytest
+
+def test_quick_sort():
+    input1 = [31, 23, 43, 56, 9]
+    input2 = []
+    assert quick_sort(input1) == [9, 23, 31, 43, 56]
+    assert quick_sort(input2) == []
+
+def quick_sort(input):
+    qs_helper(input, 0, len(input)-1)
+    return input
+
+def qs_helper(input, start, end):
+    if start < end:
+        partition = qs_partition(input, start, end)
+        # left partition
+        qs_helper(input, start, partition-1)
+        # right partition
+        qs_helper(input, partition+1, end)
+
+def qs_partition(input, start, end):
+    pivot = input[start]
+    left = start + 1
+    right = end
+    done = False
+    while not done:
+        while left <= right and input[left] < pivot:
+            left += 1
+        while input[right] > pivot and left <= right:
+            right -= 1
+        if left > right: done = True
+        else:
+            input[left], input[right] = input[right], input[left]
+
+    input[start], input[right] = input[right], input[start]
+    return right

arrays-and-strings/unique_characters.py

@@ -1,3 +1,6 @@
+# Implement an algorithm to determine if a string has all unique characters.
+# What if you can not use additional data structures?
+
 import pytest
 
 def isUnique(input):