Shell Sort

Author: Shikha-code36

Sorting-Algo/shellsort.py

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+'''
+                                        Shell Sort
+Shell sort is a generalized version of the insertion sort algorithm. It first sorts elements that are far apart from each other and successively reduces the interval between the elements to be sorted.
+
+The interval between the elements is reduced based on the sequence used. Some of the optimal sequences that can be used in the shell sort algorithm are:
+
+Shell's original sequence: N/2 , N/4 , …, 1
+Knuth's increments: 1, 4, 13, …, (3k – 1) / 2
+Sedgewick's increments: 1, 8, 23, 77, 281, 1073, 4193, 16577...4j+1+ 3·2j+ 1
+Hibbard's increments: 1, 3, 7, 15, 31, 63, 127, 255, 511…
+Papernov & Stasevich increment: 1, 3, 5, 9, 17, 33, 65,...
+Pratt: 1, 2, 3, 4, 6, 9, 8, 12, 18, 27, 16, 24, 36, 54, 81....
+'''
+def shellSort(list, n):
+
+    # Rearrange elements at each n/2, n/4, n/8, ... intervals
+    interval = n // 2
+    while interval > 0:
+        for i in range(interval, n):
+            temp = list[i]
+            j = i
+            while j >= interval and list[j - interval] > temp:
+                list[j] = list[j - interval]
+                j -= interval
+
+            list[j] = temp
+        interval //= 2
+
+
+data = [9, 8, 3, 7, 5, 6, 4, 1]
+length = len(data)
+shellSort(data, length)
+print(data) #[1, 3, 4, 5, 6, 7, 8, 9]