ai_advent_code_2024/lib/advent_code2024/solutions/day02

Day 2: Red-Nosed Reports

Problem Description

The engineers at the Red-Nosed Reindeer nuclear fusion/fission plant need help analyzing unusual data from their reactor. The data consists of reports, with each report containing a list of numbers called levels.

Rules for Safe Reports

A report is considered safe if it meets both of these criteria:

1. The levels are either all increasing or all decreasing
2. Any two adjacent levels differ by at least one and at most three

Example

7 6 4 2 1  # Safe (all decreasing by 1 or 2)
1 2 7 8 9  # Unsafe (2->7 increases by 5)
9 7 6 2 1  # Unsafe (6->2 decreases by 4)
1 3 2 4 5  # Unsafe (increasing then decreasing)
8 6 4 4 1  # Unsafe (4->4 no change)
1 3 6 7 9  # Safe (all increasing by 1-3)

Part 1 Challenge

Count how many reports in the input data are safe according to the rules above.

Input Format

Each line contains space-separated integers representing the levels in a report.

Example Solution

In the example above, 2 reports are safe.

Part 2 Challenge

The engineers discovered they forgot to tell you about the Problem Dampener - a reactor module that can tolerate a single bad level in a report. If removing any single level from an unsafe report would make it safe according to the original rules, that report should now be considered safe.

For example, in the same reports from Part 1:

7 6 4 2 1  # Safe (already safe, no removal needed)
1 2 7 8 9  # Still unsafe (no single removal helps)
9 7 6 2 1  # Still unsafe (no single removal helps)
1 3 2 4 5  # Now safe (removing 3 makes it safe)
8 6 4 4 1  # Now safe (removing one 4 makes it safe)
1 3 6 7 9  # Safe (already safe, no removal needed)

With the Problem Dampener active, 4 reports are now considered safe instead of just 2.

Count how many reports become safe when the Problem Dampener is active.