Added shell sort

Author: KyattPL

algorithms/Comparison.py

@@ -9,6 +9,7 @@
 from pigeonholeSort import pigeonhole_sort
 from quickSort import quick_sort
 from selectionSort import selection_sort
+from shellSort import shell_sort
 
 from random import randint
 
@@ -33,6 +34,8 @@
     temp = array[:]
     insertion_sort(temp)
     temp = array[:]
+    shell_sort(temp)
+    temp = array[:]
     lsd_radix_sort(temp)
     temp = array[:]
     pigeonhole_sort(temp)

algorithms/shellSort.py

@@ -0,0 +1,35 @@
+from random import random
+
+
+def shell_sort(arr):
+    comparisons = 0
+    array_accesses = 0
+    additional_space = 0
+    n = len(arr)
+    gap = n // 2
+    while gap > 0:
+        for i in range(gap, n):
+            array_accesses += 1
+            temp = arr[i]
+            j = i
+            while j >= gap and arr[j-gap] > temp:
+                array_accesses += 2
+                comparisons += 2
+                arr[j] = arr[j-gap]
+                j -= gap
+            array_accesses += 1
+            arr[j] = temp
+        gap //= 2
+
+    print("Shell sort:")
+    print("No. comparisons: " + str(comparisons) +
+          ", no. array accesses: " +
+          str(array_accesses) + ", no. additional space required: "
+          + str(additional_space))
+
+
+if __name__ == "__main__":
+    array = []
+    for i in range(20):
+        array.append(random())
+    shell_sort(array)