Merge pull request #65 from donnemartin/develop

Polish selection sort challenge and solution

sorting_searching/selection_sort/selection_sort_challenge.ipynb

@@ -35,6 +35,8 @@
     "## Constraints\n",
     "\n",
     "* Is a naiive solution sufficient (ie not stable, not based on a heap)?\n",
+    "    * Yes\n",
+    "* Are duplicates allowed?\n",
     "    * Yes"
    ]
   },
@@ -134,7 +136,7 @@
     "        assert_equal(data, [5])\n",
     "\n",
     "        print('Two or more elements')\n",
-    "        data = [5, 1, 7, 2, 6, -3, 5, 7, -1]\n",
+    "        data = [5, 1, 7, 2, 6, -3, 5, 7, -10]\n",
     "        func(data)\n",
     "        assert_equal(data, sorted(data))\n",
     "\n",
@@ -183,7 +185,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,

sorting_searching/selection_sort/selection_sort_solution.ipynb

@@ -34,6 +34,8 @@
     "## Constraints\n",
     "\n",
     "* Is a naiive solution sufficient (ie not stable, not based on a heap)?\n",
+    "    * Yes\n",
+    "* Are duplicates allowed?\n",
     "    * Yes"
    ]
   },
@@ -66,7 +68,7 @@
     "\n",
     "Complexity:\n",
     "* Time: O(n^2) average, worst, best\n",
-    "* Space: O(1) iterative, O(n) recursive (unless tail-call elimination is available, then O(1)), generally not stable\n",
+    "* Space: O(1) iterative, O(m) recursive where m is the recursion depth (unless tail-call elimination is available, then O(1)), generally not stable\n",
     "    * Note: Tail call elimination is not inherently available in Python. See the following [StackOverflow post](http://stackoverflow.com/a/13592002)."
    ]
   },
@@ -112,6 +114,9 @@
    "outputs": [],
    "source": [
     "def find_min_index(data, start):\n",
+    "    # Raises an exception if: \n",
+    "    # -data is None\n",
+    "    # -start >= len(data) - 1\n",
     "    min_index = start\n",
     "    for i in range(start + 1, len(data)):\n",
     "        if data[i] < data[min_index]:\n",
@@ -120,13 +125,16 @@
     "\n",
     "\n",
     "def swap(data, i, j):\n",
-    "    if (i != j):\n",
+    "    # Raises an exception if: \n",
+    "    # -data is None\n",
+    "    # -i or j are >= len(data)\n",
+    "    if i != j:\n",
     "        data[i], data[j] = data[j], data[i]\n",
     "\n",
     "\n",
     "def selection_sort_recursive(data, start=0):\n",
     "    if data is None:\n",
-    "        return None\n",
+    "        return\n",
     "    if start < len(data) - 1:\n",
     "        swap(data, start, find_min_index(data, start))\n",
     "        selection_sort_recursive(data, start+1)\n",
@@ -135,7 +143,7 @@
     "def selection_sort_iterative_alt(data):\n",
     "    if data is None or len(data) < 2:\n",
     "        return\n",
-    "    for i in range(0, len(data) - 1):\n",
+    "    for i in range(len(data)-1):\n",
     "        swap(data, i, find_min_index(data, i))"
    ]
   },
@@ -186,7 +194,7 @@
     "        assert_equal(data, [5])\n",
     "\n",
     "        print('Two or more elements')\n",
-    "        data = [5, 1, 7, 2, 6, -3, 5, 7, -1]\n",
+    "        data = [5, 1, 7, 2, 6, -3, 5, 7, -10]\n",
     "        func(data)\n",
     "        assert_equal(data, sorted(data))\n",
     "\n",
@@ -262,7 +270,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,

sorting_searching/selection_sort/test_selection_sort.py

@@ -20,7 +20,7 @@ class TestSelectionSort(object):
         assert_equal(data, [5])
 
         print('Two or more elements')
-        data = [5, 1, 7, 2, 6, -3, 5, 7, -1]
+        data = [5, 1, 7, 2, 6, -3, 5, 7, -10]
         func(data)
         assert_equal(data, sorted(data))