soi-manim/binary-search/binary-search-manim.py

from manim import *


class Main(Scene):
    def construct(self):
        n = 13
        k = 8

        def check(x):
            return 1 if x <= k else 0

        # initial situation
        seq = Matrix([[1] + ["?" for _ in range(n-1)] + [0]], h_buff=1.0).elements.move_to(0.5*UP)
        self.play(Create(seq))

        # source code binary search

        # while(high - low > 1){         // line_while
        #   int mid = (low + high) / 2;  // line_mid
        #   if(check(mid))               // line_check
        #       low = mid;               // line_low
        #   else
        #       high = mid;              // line_high
        # }
        code = Code(file_name="binary-search.cpp", language="c++", insert_line_no=False, style='monokai', tab_width=4, line_spacing=0.5).code
        code.move_to(4*RIGHT + 2.5*DOWN)
        while_line, mid_line, check_line, low_line, __, high_line, __ = code

        # check code
        check_code = Code(code="check(x)", language="c++", insert_line_no=False, style='monokai', tab_width=4, line_spacing=0.5).code
        check_background, check_code = check_code.move_to(2.5*UP).add_background_rectangle(opacity=1.0)
        self.play(Create(check_background), Write(check_code), Write(code))

        def pointer(name):
            arrow = Arrow(start=ORIGIN, end=UP)
            label = Tex(name).next_to(arrow, DOWN)
            return VGroup(arrow, label).scale(0.7)

        # initialize borders
        low = 0
        high = n
        low_pointer = pointer("low").next_to(seq[low], DOWN)
        high_pointer = pointer("high").next_to(seq[high], DOWN)
        self.play(Write(low_pointer), Create(high_pointer))

        mid_pointer = pointer("mid")

        def indicate_start(line):
            line.save_state()
            self.play(line.animate.scale(1.3).set_color(YELLOW))

        def indicate_end(line):
            self.play(Restore(line))

        def high_low_test():
            indicate_start(while_line)
            brace = BraceText(VGroup(*seq[low:high]), "high - low = " + str(high - low), brace_direction=UP)
            brace.label.scale(0.7)
            self.play(FadeIn(brace))
            self.wait(1)
            self.play(FadeOut(brace))
            indicate_end(while_line)

        while high_low_test() or high - low > 1:

            # calculate mid
            indicate_start(mid_line)
            mid = (low + high) // 2
            mid_pointer.next_to(seq[mid], DOWN)
            self.play(Write(mid_pointer))
            indicate_end(mid_line)

            # check
            indicate_start(check_line)

            seq[mid].add_background_rectangle(opacity=1.0)
            path = Line(start=seq[mid].get_center(), end=check_background.get_center())
            rpath = Line(start=path.get_end(), end=path.get_start())
            laser = path.copy().set_length(0.3)

            self.bring_to_back(laser)
            self.play(MoveAlongPath(laser, path))

            color = GREEN if (ans := check(mid)) else RED
            self.play(Indicate(check_code, color=color))

            self.bring_to_back(laser)
            self.play(MoveAlongPath(laser, rpath))
            self.remove(laser)

            # TODO: mark tested
            range_seq = seq[low+1:mid+1] if ans else seq[mid:high]
            self.play(*[Transform(s, Tex(ans).move_to(s)) for s in range_seq])

            indicate_end(check_line)

            if check(mid):
                # update low
                indicate_start(low_line)
                low = mid
                low_pointer.generate_target().move_to(mid_pointer)
                self.play(FadeOut(mid_pointer), MoveToTarget(low_pointer))
                indicate_end(low_line)
            else:
                # update high
                indicate_start(high_line)
                high = mid
                high_pointer.generate_target().move_to(mid_pointer)
                self.play(FadeOut(mid_pointer), MoveToTarget(high_pointer))
                indicate_end(high_line)

        self.wait(2)