Update sorts/quick_sort_3_partition.py (#2507)

* Update sorts/quick_sort_3partition.py

Another quick sort algorithm, returns a new sorted list

* Update sorts/quick_sort_3_partition.py

rename quick_sort_3partition to quick_sort_3part

* Update sorts/quick_sort_3_partition.py

rename quick_sort_3part to three_way_radix_quicksort
Three-way radix quicksort:
https://en.wikipedia.org/wiki/Quicksort#Three-way_radix_quicksort
First divide the list into three parts.
Then recursively sort the "less than" and "greater than" partitions.

* Update sorts/quick_sort_3_partition.py

Co-authored-by: Christian Clauss <cclauss@me.com>

Co-authored-by: Christian Clauss <cclauss@me.com>

Author: taseikyo

sorts/quick_sort_3_partition.py

@@ -1,4 +1,4 @@
-def quick_sort_3partition(sorting, left, right):
+def quick_sort_3partition(sorting: list, left: int, right: int) -> None:
     if right <= left:
         return
     a = i = left
@@ -18,7 +18,36 @@ def quick_sort_3partition(sorting, left, right):
     quick_sort_3partition(sorting, b + 1, right)
 
 
+def three_way_radix_quicksort(sorting: list) -> list:
+    """
+    Three-way radix quicksort:
+    https://en.wikipedia.org/wiki/Quicksort#Three-way_radix_quicksort
+    First divide the list into three parts.
+    Then recursively sort the "less than" and "greater than" partitions.
+
+    >>> three_way_radix_quicksort([])
+    []
+    >>> three_way_radix_quicksort([1])
+    [1]
+    >>> three_way_radix_quicksort([-5, -2, 1, -2, 0, 1])
+    [-5, -2, -2, 0, 1, 1]
+    >>> three_way_radix_quicksort([1, 2, 5, 1, 2, 0, 0, 5, 2, -1])
+    [-1, 0, 0, 1, 1, 2, 2, 2, 5, 5]
+    """
+    if len(sorting) <= 1:
+        return sorting
+    return (
+        three_way_radix_quicksort([i for i in sorting if i < sorting[0]])
+        + [i for i in sorting if i == sorting[0]]
+        + three_way_radix_quicksort([i for i in sorting if i > sorting[0]])
+    )
+
+
 if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod(verbose=True)
+
     user_input = input("Enter numbers separated by a comma:\n").strip()
     unsorted = [int(item) for item in user_input.split(",")]
     quick_sort_3partition(unsorted, 0, len(unsorted) - 1)