Add solutions to the first day of AOC-23

.gitignore

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 *.o
 bin
 target
+*.jar

advent-of-code-2023/01/part-1/main.kt

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+package main
+
+import java.io.File
+
+fun main() {
+    var sum = 0
+    File("../input.txt").forEachLine{
+        var firstDigit = ""
+        var lastDigit = ""
+
+        for (c in it) {
+            if (c.isDigit()) {
+                lastDigit = c.toString()
+                if (firstDigit == "") {
+                    firstDigit = c.toString()
+                }
+            }
+        }
+
+        sum += (firstDigit + lastDigit).toInt()
+    }
+    println(sum)
+}

advent-of-code-2023/01/part-1/test.txt

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+1abc2
+pqr3stu8vwx
+a1b2c3d4e5f
+treb7uchet

advent-of-code-2023/01/part-2/main.kt

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+package main
+
+import java.io.File
+
+fun main() {
+    var sum = 0
+    File("../input.txt").forEachLine{
+        var firstDigit = ""
+        var lastDigit = ""
+
+        for (c in replaceStrWithDigits(it)) {
+            if (c.isDigit()) {
+                lastDigit = c.toString()
+                if (firstDigit == "") {
+                    firstDigit = c.toString()
+                }
+            }
+        }
+
+        sum += (firstDigit + lastDigit).toInt()
+    }
+    println(sum)
+}
+
+fun replaceStrWithDigits(line: String): String {
+    var s = line
+    var words = arrayOf("one", "two", "three", "four", "five", "six", "seven", "eight", "nine")
+    var i = 0
+    while (i < s.length) {
+        for (w in words.indices) {
+            if (s.slice(i..s.length-1).startsWith(words[w])) {
+                s = s.replaceRange(i, i + 1, (w + 1).toString())
+                break
+            }
+        }
+        i += 1
+    }
+    return s
+}

advent-of-code-2023/01/part-2/test.txt

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+two1nine
+eightwothree
+abcone2threexyz
+xtwone3four
+4nineeightseven2
+zoneight234
+7pqrstsixteen

advent-of-code-2023/01/readme.md

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+# Day 1: Trebuchet?!
+
+Something is wrong with global snow production, and you've been selected to take a look.
+The Elves have even given you a map; on it, they've used stars to mark the top fifty locations
+that are likely to be having problems.
+
+You've been doing this long enough to know that to restore snow operations,
+you need to check all fifty stars by December 25th.
+
+Collect stars by solving puzzles. Two puzzles will be made available on each day in the Advent calendar;
+the second puzzle is unlocked when you complete the first. Each puzzle grants one star. Good luck!
+
+You try to ask why they can't just use a weather machine ("not powerful enough")
+and where they're even sending you ("the sky") and why your map looks mostly blank
+("you sure ask a lot of questions") and hang on did you just say the sky
+("of course, where do you think snow comes from") when you realize that the Elves
+are already loading you into a trebuchet ("please hold still, we need to strap you in").
+
+As they're making the final adjustments, they discover that their calibration document
+(your puzzle input) has been amended by a very young Elf who was apparently just excited to show off
+her art skills. Consequently, the Elves are having trouble reading the values on the document.
+
+The newly-improved calibration document consists of lines of text;
+each line originally contained a specific calibration value that the Elves now need to recover.
+On each line, the calibration value can be found by combining the first digit and the last digit
+(in that order) to form a single two-digit number.
+
+For example:
+
+```
+1abc2
+pqr3stu8vwx
+a1b2c3d4e5f
+treb7uchet
+```
+
+In this example, the calibration values of these four lines are `12`, `38`, `15`, and `77`.
+Adding these together produces `142`.
+
+Consider your entire calibration document. What is the sum of all of the calibration values?
+
+## Part Two
+
+Your calculation isn't quite right. It looks like some of the digits are actually spelled out with letters:
+`one`, `two`, `three`, `four`, `five`, `six`, `seven`, `eight`, and `nine` also count as valid "digits".
+
+Equipped with this new information, you now need to find the real first and last digit on each line. For example:
+
+```
+two1nine
+eightwothree
+abcone2threexyz
+xtwone3four
+4nineeightseven2
+zoneight234
+7pqrstsixteen
+```
+
+In this example, the calibration values are `29`, `83`, `13`, `24`, `42`, `14`, and `76`.
+Adding these together produces `281`.
+
+What is the sum of all of the calibration values?

advent-of-code-2023/readme.md

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+# Advent of code 2023
+
+My goal is to learn the basics of Kotlin.
+I have never worked with Kotlin or Java before.