Knuth/ Fisher-Yates Shuffle Animation

scene.py

"""
Knuth/ Fisher-Yates shuffle algorithm visualized with the manim library.

Install manim (preferably in a virtual environment),
$ pip install manim

Generate the animation play the resulting mp4 file,
$ manim -pql scene.py KnuthShuffle

To generate a higher quality animation once you're done testing the code (takes more time to execute),
$ manim -qh scene.py KnuthShuffle
"""
from manim import *
import random

class KnuthShuffle(Scene):
    def construct(self):
        # Initial list
        data = ["A", "B", "C", "D", "E"]

        # Create text objects for the list elements
        elements = [Text(str(num)) for num in data]
        # Create white square outlines for the elements
        outlines = [Square(side_length=1.2, color=WHITE) for _ in data]

        for i, (element, outline) in enumerate(zip(elements, outlines)):
            element.move_to(DOWN * 1.2 + RIGHT * (i * 1.2 - 4) + 1.2)
            outline.move_to(element.get_center())

        self.play(*[Write(element) for element in elements])
        self.play(*[Create(outline) for outline in outlines])
        self.wait()

        for i in range(len(data) - 1, 0, -1):
            # Random index between 0 and i
            j = random.randint(0, i)

            if i != j:
                arrow = CurvedDoubleArrow(elements[i].get_bottom() + DOWN * 0.5, elements[j].get_bottom() + DOWN * 0.5, color=RED, angle=-TAU/4)
            else:
                arrow = CurvedDoubleArrow(elements[i].get_bottom() + DOWN * 0.5 + RIGHT * 0.5, elements[j].get_bottom() + DOWN * 0.5 + LEFT * 0.5, color=RED, angle=-TAU/4)

            self.play(FadeIn(arrow))
            self.wait(0.5)

            # Swap the elements in the list
            data[i], data[j] = data[j], data[i]

            # Animate the swap
            self.play(
                elements[i].animate.move_to(elements[j].get_center()),
                elements[j].animate.move_to(elements[i].get_center()),
                outlines[i].animate.move_to(outlines[j].get_center()),
                outlines[j].animate.move_to(outlines[i].get_center())
            )
            # Update their positions in the list
            elements[i], elements[j] = elements[j], elements[i]
            outlines[i], outlines[j] = outlines[j], outlines[i]
            self.wait(0.5)

            self.play(outlines[i].animate.set_fill(PINK, opacity=0.2))
            # Remove the arrow
            self.play(FadeOut(arrow))

        # Final wait before ending the scene
        self.wait(2)

knuth_shuffle.mp4