[Language: C#]

This isn’t the most performant or elegant, it’s the first one that worked. I have 3 kids and a full time job. If I get through any of these, it’ll be first pass through and first try that gets the correct answer.

Part 1 was very easy, just iterated the string checking if the char was a digit. Ditto for the last, by reversing the string. Part 2 was also not super hard, I settled on re-using the iterative approach, checking each string lookup value first (on a substring of the current char), and if the current char isn’t the start of a word, then checking if the char was a digit. Getting the last number required reversing the string and the lookup map.

Part 1:

var list = new List((await File.ReadAllLinesAsync(@".\Day 1\PuzzleInput.txt")));

int total = 0;
foreach (var item in list)
{
    //forward
    string digit1 = string.Empty;
    string digit2 = string.Empty;


    foreach (var c in item)
    {
        if ((int)c >= 48 && (int)c <= 57)
        {
            digit1 += c;
        
            break;
        }
    }
    //reverse
    foreach (var c in item.Reverse())
    {
        if ((int)c >= 48 && (int)c <= 57)
        {
            digit2 += c;

            break;
        }

    }
    total += Int32.Parse(digit1 +digit2);
}

Console.WriteLine(total);

Part 2:

var list = new List((await File.ReadAllLinesAsync(@".\Day 1\PuzzleInput.txt")));
var numbers = new Dictionary() {
    {"one" ,   1}
    ,{"two" ,  2}
    ,{"three" , 3}
    ,{"four" , 4}
    ,{"five" , 5}
    ,{"six" , 6}
    ,{"seven" , 7}
    ,{"eight" , 8}
    , {"nine" , 9 }
};
int total = 0;
string digit1 = string.Empty;
string digit2 = string.Empty;
foreach (var item in list)
{
    //forward
    digit1 = getDigit(item, numbers);
    digit2 = getDigit(new string(item.Reverse().ToArray()), numbers.ToDictionary(k => new string(k.Key.Reverse().ToArray()), k => k.Value));
    total += Int32.Parse(digit1 + digit2);
}

Console.WriteLine(total);

string getDigit(string item,                 Dictionary numbers)
{
    int index = 0;
    int digit = 0;
    foreach (var c in item)
    {
        var sub = item.AsSpan(index++);
        foreach(var n in numbers)
        {
            if (sub.StartsWith(n.Key))
            {
                digit = n.Value;
                goto end;
            }
        }

        if ((int)c >= 48 && (int)c <= 57)
        {
            digit = ((int)c) - 48;
            break;
        }
    }
    end:
    return digit.ToString();
}