AoC ‘24 - Day 1: Historian Hysteria (C# & Python) #Spoilers

Todays challenge was quite simple:

Part 1:
To solve the problem we had to

• create 2 lists of numbers from the string input,
• order them ascending
• foreach number in List1 get the same index in List2 and find the distance between the two numbers.
• and then sum the distances up

Easy Right.

Part 2:

This was a little trickier but the main concept of my solution was :

• create a dictionary where the key is the number in listA, the value used the Count() method to count all the numbers in listB that were the same as the key (number at same index as listA).

• then it’s just a simple case of multiplying the keys by the values and summing the totals.

Csharp Parts 1 and 2:

var input = File.ReadAllLines("./input_1.txt")
    .Select(s => s.Split([' '], StringSplitOptions.RemoveEmptyEntries)).ToList();

var lists = ProcessLines(input);

Part1(lists.list1, lists.list2);

Part2(lists.list1, lists.list2);
return;


void Part1(List<int> list1, List<int> list2)
{
    var ordered1 = list1.OrderBy(x => x).ToList();
    var ordered2 = list2.OrderBy(x => x).ToList();
    var totals = ordered1
        .Select((t, i) => Math.Abs(t - ordered2[i]))
        .Select(difference => (long)difference)
        .ToList();


    Console.WriteLine("Sum of differences: " + totals.Sum());
}


void Part2(List<int> list1, List<int> list2)
{
    var counts = list1.ToDictionary(
        number => number,
        number => list2.Count(x => x == number)
    );

    var sum = counts.Sum(x => x.Value * x.Key);
    Console.WriteLine("Sum of counts: " + sum);
}

(List<int> list1, List<int> list2) ProcessLines(List<string[]> rows)
{
    var list1 = new List<int>();
    var list2 = new List<int>();

    foreach (var row in rows)
    {
        list1.Add(int.Parse(row[0]));
        list2.Add(int.Parse(row[1]));
    }

    return (list1, list2);
}

Part 1 - Python

Same concept different syntax - lot
More concise using the built-in zip function, and list comprehension functionality.

def get_steps(list1, list2):
    totals = [abs(value - partner_item)
              for value, partner_item in zip(list1, list2)]
    print("Sum Total:", sum(totals))


def read_input(file_name):
    list1, list2 = zip(*((int(num1), int(num2))
                       for num1, num2 in (line.split() for line in open(file_name))))
    return sorted(list1), sorted(list2)


list1, list2 = read_input("input.txt")

get_steps(list1, list2)

Part 2 - In Progress (it got late)⏰