Uiua

Took me a bit longer to get this one but still quite simple overall.
Spent quite some time on getting to know the try and assert operators better.

Run with example input here

# Get the indices matching the ascending/
# descending criteria
CheckAsc ← ≡°□⍚(⍣(⊸⍤.≍⍆.)⍣(⊸⍤.≍⇌⍆.)0)
# Get the indices matching the distance criteria
CheckDist ← ≡°□⍚(⍣(⊸⍤.≠1∈:0)0×⊓≥≤1,3⌵⧈-)
Split     ← ⊙(▽≠1)▽,,

PartOne ← (
  &rs ∞ &fo "input-2.txt"
  ⊜(□⊜⋕≠@ .)≠@\n.
  CheckAsc.
  ▽
  CheckDist
  ⧻⊚
)

PartTwo ← (
  &rs ∞ &fo "input-2.txt"
  ⊜(□⊜⋕≠@ .)≠@\n.
  CheckAsc.
  Split
  CheckDist.
  Split
  ⊙(⊂)
  ⧻
  :
  ⍚(≡(▽:°⊟)⍜¤⊞⊟:≠1⊞=.⇡⧻.)
  ≡(⧻⊚CheckDist▽CheckAsc.°□)
  +⧻◴⊚
)

&p "Day 2:"
&pf "Part 1: "
&p PartOne
&pf "Part 2: "
&p PartTwo

R (R-Wasm)

input = file('input2024day2.txt',open='r')
lines = readLines(input)
library(stringr)
safe = 0
safe2 = 0
for (ln in lines){
  vals = as.numeric(unlist(str_split(ln,' ')))
  diffs = diff(vals)
  cond1 = min(diffs) > 0 || max(diffs) < 0
  cond2 = max(abs(diffs)) < 4
  if (cond1 && cond2){
    safe = safe + 1
  }
  else { #Problem Dampener
    dampen = FALSE
    for (omit in -1:-length(vals)){
      diffs = diff(vals[omit])
      cond1 = min(diffs) > 0 || max(diffs) < 0
      cond2 = max(abs(diffs)) < 4
      if (cond1 && cond2){
        dampen = TRUE
      }
    }
    if (dampen){
      safe2 = safe2 + 1}
  }
}
print (safe) #Part 1
print (safe + safe2) #Part 2

Kotlin:

import kotlin.math.abs
import kotlin.math.sign

data class Report(val levels: List<Int>) {
    fun isSafe(withProblemDampener: Boolean): Boolean {
        var orderSign = 0.0f  // - 1 is descending; +1 is ascending

        levels.zipWithNext().forEachIndexed { index, level ->
            val difference = (level.second - level.first).toFloat()
            if (orderSign == 0.0f) orderSign = sign(difference)
            if (sign(difference) != orderSign || abs(difference) !in 1.0..3.0) {
                // With problem dampener: Drop either element in the pair or the first element from the original list and check if the result is now safe.
                return if (withProblemDampener) {
                    Report(levels.drop(1)).isSafe(false) || Report(levels.withoutElementAt(index)).isSafe(false) || Report(levels.withoutElementAt(index + 1)).isSafe(false)
                }  else false
            }
        }

        return true
    }
}

fun main() {
    fun part1(input: List<String>): Int = input.map { Report(it.split(" ").map { it.toInt() }).isSafe(false) }.count { it }

    fun part2(input: List<String>): Int = input.map { Report(it.split(" ").map { it.toInt() }).isSafe(true) }.count { it }

    // Or read a large test input from the `src/Day01_test.txt` file:
    val testInput = readInput("Day02_test")
    check(part1(testInput) == 2)
    check(part2(testInput) == 4)

    // Read the input from the `src/Day01.txt` file.
    val input = readInput("Day02")
    part1(input).println()
    part2(input).println()
}

The Report#isSafe method essentially solves both parts.

I've had a bit of a trip up in part 2:

I initially only checked, if the report was safe, if either elements in the pair were to be removed. But in the edge case, that the first pair has different monotonic behaviour than the rest, the issue would only be detected by the second pair with indices (2, 3), whilst removing the first element in the list would yield a safe report.

Rust

Turned out alright, I am looking forward to seeing what 2d coordinate grid code I can cannibalize from last year's solutions 😄

Github link

C#

using MathNet.Numerics.LinearAlgebra;
public class Day02 : Solver
{
  private ImmutableList<Vector<Double>> data;

  public void Presolve(string input)
  {
    data = input.Trim().Split("\n")
        .Select(
            line => Vector<Double>.Build.DenseOfEnumerable(line.Split(' ').Select(double.Parse))
        ).ToImmutableList();
  }

  private bool IsReportSafe(Vector<Double> report) {
    Vector<Double> delta = report.SubVector(1, report.Count - 1)
        .Subtract(report.SubVector(0, report.Count - 1));
    return (delta.ForAll(x => x > 0) || delta.ForAll(x => x < 0))
        && Vector<Double>.Abs(delta).Max() <= 3;
  }

  private bool IsDampenedReportSafe(Vector<Double> report) {
    for (Double i = 0; i < report.Count; ++i) {
      var dampened = Vector<Double>.Build.DenseOfEnumerable(
            report.EnumerateIndexed()
                .Where(item => item.Item1 != i)
                .Select(item => item.Item2));
      if (IsReportSafe(dampened)) return true;
    }
    return false;
  }

  public string SolveFirst() => data.Where(IsReportSafe).Count().ToString();

  public string SolveSecond() => data.Where(IsDampenedReportSafe).Count().ToString();
}