Add flash sort algorithm implementation

sorts/flash_sort.py

@@ -0,0 +1,100 @@
+"""
+Implementation of Flash Sort in Python
+Author: Aman Gupta
+
+For doctests, run the following command:
+python3 -m doctest -v flash_sort.py
+
+For manual testing, run:
+python3 flash_sort.py
+"""
+
+from __future__ import annotations
+from collections.abc import Callable
+
+
+class FlashSort:
+    def __init__(self, arr: list[int], n_classes: int, sort_key: Callable[[int], int] = lambda x: x):
+        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()
+        >>> arr
+        [2, 2, 2]
+        """
+        if self.n <= 1:
+            return
+
+        min_val = min(self.arr, key=self.sort_key)
+        max_val = max(self.arr, key=self.sort_key)
+
+        if self.sort_key(min_val) == self.sort_key(max_val):
+            return
+
+        count = [0] * self.n_classes  # Renamed variable `l` to `count`
+        c1 = (self.n_classes - 1) / (self.sort_key(max_val) - self.sort_key(min_val))
+
+        # Classification step
+        for i in range(self.n):
+            k = int(c1 * (self.sort_key(self.arr[i]) - self.sort_key(min_val)))
+            count[k] += 1
+
+        # Cumulative step
+        for i in range(1, self.n_classes):
+            count[i] += count[i - 1]
+
+        # Permutation step
+        i, nmove, flash = 0, 0, self.arr[0]
+        while nmove < self.n:
+            while i >= count[int(c1 * (self.sort_key(flash) - self.sort_key(min_val)))]:
+                i += 1
+                flash = self.arr[i]
+            k = int(c1 * (self.sort_key(flash) - self.sort_key(min_val)))
+
+            while i != count[k]:
+                k = int(c1 * (self.sort_key(flash) - self.sort_key(min_val)))
+                hold = self.arr[count[k] - 1]
+                self.arr[count[k] - 1] = flash
+                flash = hold
+                count[k] -= 1
+                nmove += 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)