Advent of Code - Day 1

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My Code

left = []
right = []
with open("day1.txt") as f:
    for line in f.readlines():
        line.replace("\n","")
        curr = line.split("   ")
        left.append(int(curr[0]))
        right.append(int(curr[1]))

left.sort()
right.sort()

right_count = {}
for i in range (len(right)):
    if right[i] in right_count.keys():
        right_count[right[i]] += 1
    else:
        right_count[right[i]] = 1 

score = 0
for i in range(len(left)):
    if left[i] in right_count.keys():
        score += left[i] * right_count[left[i]]
    else:
        score += left[i] * 0

print(score)

ChatGPT’s Improved Code

from collections import Counter

# Initialize lists
left = []
right = []

# Read and process the file
with open("day1.txt") as f:
    for line in f:
        # Strip newline characters and split the line into parts
        curr = line.strip().split("   ")
        # Append values to respective lists
        left.append(int(curr[0]))
        right.append(int(curr[1]))

# Sort the lists (not strictly necessary for the given logic but kept if needed elsewhere)
left.sort()
right.sort()

# Use Counter to simplify counting occurrences in the 'right' list
right_count = Counter(right)

# Calculate the score
score = sum(
    left[i] * right_count.get(left[i], 0) 
    for i in range(len(left))
)

# Print the final score
print(score)

What I Learned

strip()

• Newline characters can be stripped in a one line function call strip().

• Strip() with no arguments removes leading and trailing white spaces in a string.

• You can also pass arguments to strip() to remove specified characters:

  my_string = "hello there !!!!! .."
  my_stripped_string = my_string.strip("!.")
  print(my_stripped_string)
  # Outputs "hello there "

collections.Counter

• Collections.Counter() tallies the number of occurrences of elements in a list. The input is a list and the output is a dictionary where each element in the list is a key and the value is the number of times the element occurs in the list.

• Counter items return 0 count for missing elements instead of raising a KeyError

• Elements can have 0 count, negative count

• Removing a key from the counter will remove all instances of the key in the iterator generated by counter.elements()

• You can also use Counter to generate lists with a certain number of elements. For example:

  a = Counter(a=3,b=2)
  sorted(a.elements())
  # outputs ['a','a','a','b','b']

dict.get()

• We can use dict.get() when retreiving elements from a hashset to avoid KeyError.
• The first argument to get() is the key you want to retrieve, and the second argument is the default return value if the key is not found.

sum()

• We can use the sum() function to sum a certain operation over iterations in a loop.

• sum() takes an iterator as input in the form of:

  sum([action] for i in range ([number of times]))

• This will be the sum off all [action]s across [number of times] iterations

Callista Krebs, 2024