Day 6: Wait for It


Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
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FAQ

  • @purplemonkeymad
    link
    26 months ago

    That was so much better than yesterday. Went with algebra but looks like brute force would have worked.

    python
    import re
    import argparse
    import math
    
    # i feel doing this with equations is probably the
    # "fast" way.
    
    # we can re-arange stuff so we only need to find the point
    # the line crosses the 0 line
    
    # distance is speed * (time less time holding the button (which is equal to speed)):
    # -> d = v * (t - v)
    # -> v^2 -vt +d = 0
    
    # -> y=0 @ v = t +- sqrt( t^2 - 4d) / 2
    
    def get_cross_points(time:int, distance:int) -> list | None:
        pre_root = time**2 - (4 * distance)
        if pre_root < 0:
            # no solutions
            return None
        if pre_root == 0:
            # one solution
            return [(float(time)/2)]
        sqroot = math.sqrt(pre_root)
        v1 = (float(time) + sqroot)/2
        v2 = (float(time) - sqroot)/2
        return [v1,v2]
    
    def float_pair_to_int_pair(a:float,b:float):
        # if floats are equal to int value, then we need to add one to value
        # as we are looking for values above 0 point
        
        if a > b:
            # lower a and up b
            if a == int(a):
                a -= 1
            if b == int(b):
                b += 1
    
            return [math.floor(a),math.ceil(b)]
        if a < b:
            if a == int(a):
                a += 1
            if b == int(b):
                b -= 1
            return [math.floor(b),math.ceil(a)]
    
    def main(line_list: list):
        time_section,distance_section = line_list
        if (args.part == 1):
            time_list = filter(None , re.split(' +',time_section.split(':')[1]))
            distance_list = filter(None ,  re.split(' +',distance_section.split(':')[1]))
            games = list(zip(time_list,distance_list))
        if (args.part == 2):
            games = [ [time_section.replace(' ','').split(':')[1],distance_section.replace(' ','').split(':')[1]] ]
        print (games)
        total = 1
        for t,d in games:
            cross = get_cross_points(int(t),int(d))
            cross_int = float_pair_to_int_pair(*cross)
            print (cross_int)
            total *= cross_int[0] - cross_int[1] +1
        
        print(f"total: {total}")
    
    if __name__ == "__main__":
        parser = argparse.ArgumentParser(description="day 6 solver")
        parser.add_argument("-input",type=str)
        parser.add_argument("-part",type=int)
        args = parser.parse_args()
        filename = args.input
        if filename == None:
            parser.print_help()
            exit(1)
        file = open(filename,'r')
        main([line.rstrip('\n') for line in file.readlines()])
        file.close()