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Day 6

Lanternfish

view the Advent of Code 2021 Day 6 challenge

Setup

# Setup - load any packages
import numpy as np
from collections import Counter

Load the data

def LoadData(filename):
    return np.loadtxt(filename, dtype='int', delimiter=',')

Part 1

def GenerateLanternFish(fish, days):
    # fish = numpy array of the starting fish
    # days = int of days to run the model for
    
    for day in range(days):
        #for each day in days

        # decrease fish age by 1
        fish=fish-1
        
        # calculate how many new fish need to be created (age < 0)
        new_fish_count=(fish < 0).sum()
        
        # reset any fish that have just made new fish to 6
        fish=np.where(fish <0 , 6, fish)
        
        # add the new fish with a starting value of 8
        if new_fish_count>0:
            # create an array of new fish with age 8
            new_fish=np.full(new_fish_count, 8)
            fish=np.append(fish, new_fish)
            
    # return the number of fish    
    return fish.size
   

day6_raw=LoadData('day6_data.txt')
p1_answer=GenerateLanternFish(day6_raw, 80)
print(f'answer = {p1_answer}') 

answer = 387413

Part 2

view the Advent of Code 2021 Day 6 challenge Part 2

Alternative approach for part 2 as part 1s brute force is too resource intensive for 256 days. (Should have done it this way first)

def GenerateLanternFish(fish, days):
    # add the fish to a counter 
    count = Counter(fish)
    
    for day in range(days):
        # loop through each day
        # store fish on zero as these become 6 and also generate new fish with count of 8
        mothers = count[0]
        
        # now move each count down 1 to age the fish
        count[0] = count[1]
        count[1] = count[2]
        count[2] = count[3]
        count[3] = count[4]
        count[4] = count[5]
        count[5] = count[6]
        count[6] = count[7]
        
        # Add on the fish that reset becuase they had fish
        count[6] = count[6] + mothers
        count[7] = count[8]
        
        # Add the newly born fish
        count[8] = mothers

    # return the sum of all fish
    return sum(count.values())

day6_raw=LoadData('day6_data.txt')
p2_answer=GenerateLanternFish(day6_raw, 256)
print(f'answer = {p2_answer}') 

answer = 1738377086345