From 981f775d97d516664b69f0795f987bc2ca540d0f Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Sat, 18 Jun 2016 22:17:09 -0400
Subject: [PATCH] Polish quicksort challenge and solution

Update constraints and code.
---
 .../quick_sort/quick_sort_challenge.ipynb         |  4 +++-
 .../quick_sort/quick_sort_solution.ipynb          | 15 +++++++++------
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/sorting_searching/quick_sort/quick_sort_challenge.ipynb b/sorting_searching/quick_sort/quick_sort_challenge.ipynb
index cdd768d..7b317d1 100644
--- a/sorting_searching/quick_sort/quick_sort_challenge.ipynb
+++ b/sorting_searching/quick_sort/quick_sort_challenge.ipynb
@@ -35,6 +35,8 @@
     "## Constraints\n",
     "\n",
     "* Is a naiive solution sufficient (ie not in-place)?\n",
+    "    * Yes\n",
+    "* Are duplicates allowed?\n",
     "    * Yes"
    ]
   },
@@ -162,7 +164,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,
diff --git a/sorting_searching/quick_sort/quick_sort_solution.ipynb b/sorting_searching/quick_sort/quick_sort_solution.ipynb
index 3285119..c49db1c 100644
--- a/sorting_searching/quick_sort/quick_sort_solution.ipynb
+++ b/sorting_searching/quick_sort/quick_sort_solution.ipynb
@@ -35,6 +35,8 @@
     "## Constraints\n",
     "\n",
     "* Is a naiive solution sufficient (ie not in-place)?\n",
+    "    * Yes\n",
+    "* Are duplicates allowed?\n",
     "    * Yes"
    ]
   },
@@ -96,16 +98,17 @@
     "def quick_sort(data):\n",
     "    if data is None or len(data) < 2:\n",
     "        return data\n",
+    "    equal = []\n",
     "    left = []\n",
     "    right = []\n",
     "    pivot_index = len(data) // 2\n",
     "    pivot_value = data[pivot_index]\n",
     "\n",
     "    # Build the left and right partitions\n",
-    "    for i in range(0, len(data)):\n",
-    "        if i == pivot_index:\n",
-    "            continue\n",
-    "        if data[i] < pivot_value:\n",
+    "    for i in range(len(data)):\n",
+    "        if data[i] == pivot_value:\n",
+    "            equal.append(data[i])\n",
+    "        elif data[i] < pivot_value:\n",
     "            left.append(data[i])\n",
     "        else:\n",
     "            right.append(data[i])\n",
@@ -113,7 +116,7 @@
     "    # Recursively apply quick_sort\n",
     "    left = quick_sort(left)\n",
     "    right = quick_sort(right)\n",
-    "    return left + [pivot_value] + right"
+    "    return left + equal + right"
    ]
   },
   {
@@ -219,7 +222,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,