add pigeonhole sort

Author: Liam

README.md

@@ -277,6 +277,7 @@ If you want to uninstall algorithms, it is as simple as:
     - [meeting_rooms](algorithms/sort/meeting_rooms.py)
     - [merge_sort](algorithms/sort/merge_sort.py)
     - [pancake_sort](algorithms/sort/pancake_sort.py)
+    - [pigeonhole_sort](algorithms/sort/pigeonhole_sort.py)
     - [quick_sort](algorithms/sort/quick_sort.py)
     - [radix_sort](algorithms/sort/radix_sort.py)
     - [selection_sort](algorithms/sort/selection_sort.py)

algorithms/sort/pigeonhole_sort.py

@@ -0,0 +1,28 @@
+"""
+
+https://en.wikipedia.org/wiki/Pigeonhole_sort
+
+Time complexity: O(n + Range) where n = number of elements and Range = possible values in the array
+
+Suitable for lists where the number of elements and key values are mostly the same.
+
+"""
+
+
+def pigeonhole_sort(arr):
+    Max = max(arr)
+    Min = min(arr)
+    size = Max - Min + 1
+
+    holes = [0]*size
+
+    for i in arr:
+        holes[i-Min] += 1
+
+    i = 0
+    for count in range(size):
+        while holes[count] > 0:
+            holes[count] -= 1
+            arr[i] = count + Min
+            i += 1
+    return arr

tests/test_sort.py

@@ -9,6 +9,7 @@
     insertion_sort,
     merge_sort,
     pancake_sort,
+    pigeonhole_sort,
     quick_sort,
     selection_sort,
     bucket_sort,
@@ -70,6 +71,10 @@ def test_merge_sort(self):
     def test_pancake_sort(self):
         self.assertEqual([1, 5, 23, 57, 65, 1232],
                          pancake_sort([1, 5, 65, 23, 57, 1232]))
+    
+    def test_pigeonhole_sort(self):
+        self.assertEqual([1, 5, 23, 57, 65, 1232],
+                         pigeonhole_sort([1, 5, 65, 23, 57, 1232]))
 
     def test_quick_sort(self):
         self.assertEqual([1, 5, 23, 57, 65, 1232],