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)
  • Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ , pastebin, or github (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)

FAQ

  • @purplemonkeymad
    2•7 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()