Add flash sort algorithm implementation

sorts/flash_sort.py

@@ -0,0 +1,123 @@
+from __future__ import annotations
+
+from collections.abc import Callable
+
+"""
+Implementation of Flash Sort in Python
+Author: Yash Kiradoo
+
+For doctests, run the following command:
+python3 -m doctest -v flash_sort.py
+
+For manual testing, run:
+python3 flash_sort.py
+"""
+
+class FlashSort:
+    def __init__(
+        self,
+        arr: list[int],
+        n_classes: int,
+        sort_key: Callable[[int], int] = lambda item: item,
+    ) -> None:  # Added return type hint
+        self.arr = arr
+        self.n = len(arr)
+        self.n_classes = n_classes
+        self.sort_key = sort_key
+
+    def flash_sort(self) -> None:
+        """
+        Performs flash sort on the array in-place.
+
+        >>> arr = [5, 3, 8, 6, 2, 7, 4, 1]
+        >>> sorter = FlashSort(arr, n_classes=5)
+        >>> sorter.flash_sort()
+        >>> arr
+        [1, 2, 3, 4, 5, 6, 7, 8]
+
+        >>> arr = [1]
+        >>> sorter = FlashSort(arr, n_classes=1)
+        >>> sorter.flash_sort()
+        >>> arr
+        [1]
+
+        >>> arr = [2, 2, 2]
+        >>> sorter = FlashSort(arr, n_classes=2)
+        >>> sorter.flash_sort()
+        [2, 2, 2]
+        """
+        if self.n <= 1:
+            return
+
+        min_value = min(self.arr, key=self.sort_key)
+        max_value = max(self.arr, key=self.sort_key)
+
+        if self.sort_key(min_value) == self.sort_key(max_value):
+            return
+
+        count_classes = [0] * self.n_classes  # Renamed variable `count` for clarity
+        classification_factor = (self.n_classes - 1) / (
+            self.sort_key(max_value) - self.sort_key(min_value)
+        )
+
+        # Classification step
+        for i in range(self.n):
+            class_index = int(
+                classification_factor
+                * (self.sort_key(self.arr[i]) - self.sort_key(min_value))
+            )
+            count_classes[class_index] += 1
+
+        # Cumulative step
+        for i in range(1, self.n_classes):
+            count_classes[i] += count_classes[i - 1]
+
+        # Permutation step
+        i, num_moves, flash_item = 0, 0, self.arr[0]
+        while num_moves < self.n:
+            while (
+                i
+                >= count_classes[
+                    int(
+                        classification_factor
+                        * (self.sort_key(flash_item) - self.sort_key(min_value))
+                    )
+                ]
+            ):
+                i += 1
+                flash_item = self.arr[i]
+            class_index = int(
+                classification_factor
+                * (self.sort_key(flash_item) - self.sort_key(min_value))
+            )
+
+            while i != count_classes[class_index]:
+                class_index = int(
+                    classification_factor
+                    * (self.sort_key(flash_item) - self.sort_key(min_value))
+                )
+                temp_item = self.arr[count_classes[class_index] - 1]
+                self.arr[count_classes[class_index] - 1] = flash_item
+                flash_item = temp_item
+                count_classes[class_index] -= 1
+                num_moves += 1
+
+        # Final step: Insertion sort to finish
+        for i in range(1, self.n):
+            key_item = self.arr[i]
+            j = i - 1
+            while j >= 0 and self.arr[j] > key_item:
+                self.arr[j + 1] = self.arr[j]
+                j -= 1
+            self.arr[j + 1] = key_item
+
+
+if __name__ == "__main__":
+    user_input = input("Enter numbers separated by a comma:\n").strip()
+    if user_input == "":
+        unsorted = []
+    else:
+        unsorted = [int(item.strip()) for item in user_input.split(",")]
+    sorter = FlashSort(unsorted, n_classes=5)
+    sorter.flash_sort()
+    print(unsorted)