Added strand sort

sorts/strand_sort.py

@@ -0,0 +1,60 @@
+from functools import partial
+import operator
+
+
+def strand_sort(arr: list, solution: list, _operator: callable):
+    """
+    Strand sort implementation
+    source: https://en.wikipedia.org/wiki/Strand_sort
+
+    :param arr: Unordered input list
+    :param solution: Ordered output list
+    :param _operator: Operator lt/gt to specify ascent/descent version
+
+    Examples:
+    >>> solution_1 = []
+    >>> strand_sort([4, 2, 5, 3, 0, 1], solution_1, operator.gt)
+    >>> solution_1
+    [0, 1, 2, 3, 4, 5]
+
+    >>> solution_2 = []
+    >>> strand_sort([4, 2, 5, 3, 0, 1], solution_2, operator.lt)
+    >>> solution_2
+    [5, 4, 3, 2, 1, 0]
+    """
+    if not arr:
+        return
+
+    sublist = [arr.pop(0)]
+    for i, item in enumerate(arr):
+        if _operator(item, sublist[-1]):
+            sublist.append(item)
+            arr.pop(i)
+
+    #  merging sublist into solution list
+    if not solution:
+        solution.extend(sublist)
+    else:
+        while sublist:
+            item = sublist.pop(0)
+            for i, xx in enumerate(solution):
+                if not _operator(item, xx):
+                    solution.insert(i, item)
+                    break
+            else:
+                solution.append(item)
+
+    strand_sort(arr, solution, _operator)
+
+
+strand_asc = partial(strand_sort, _operator=operator.gt)
+strand_desc = partial(strand_sort, _operator=operator.lt)
+
+if __name__ == "__main__":
+    solution = []
+    strand_asc([4, 3, 5, 1, 2], solution)
+    assert solution == [1, 2, 3, 4, 5]
+
+    solution = []
+    strand_desc([4, 3, 5, 1, 2], solution)
+    assert solution == [5, 4, 3, 2, 1]