From 7bf66496af3b31dee24310a8360641791f22938d Mon Sep 17 00:00:00 2001
From: Aaron Manning <contact@aaronmanning.net>
Date: Fri, 6 Dec 2024 18:18:34 +1100
Subject: [PATCH] day 2

---
 day-02/Cargo.lock  |  7 +++++
 day-02/Cargo.toml  |  6 +++++
 day-02/src/main.rs | 65 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+)
 create mode 100644 day-02/Cargo.lock
 create mode 100644 day-02/Cargo.toml
 create mode 100644 day-02/src/main.rs

diff --git a/day-02/Cargo.lock b/day-02/Cargo.lock
new file mode 100644
index 0000000..5de1616
--- /dev/null
+++ b/day-02/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day-02"
+version = "0.1.0"
diff --git a/day-02/Cargo.toml b/day-02/Cargo.toml
new file mode 100644
index 0000000..b450e6a
--- /dev/null
+++ b/day-02/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day-02"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day-02/src/main.rs b/day-02/src/main.rs
new file mode 100644
index 0000000..09e1f44
--- /dev/null
+++ b/day-02/src/main.rs
@@ -0,0 +1,65 @@
+const INPUT: &str = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/input.txt"));
+
+fn main() {
+    let mut safe = 0;
+    for line in INPUT.lines() {
+        let report = line
+            .split_whitespace()
+            .filter_map(|num| {
+                str::parse::<u8>(num).ok()
+            });
+
+        safe += u16::from(is_safe(report));
+    }
+
+    println!("Part 1: {}", safe);
+
+    let mut still_safe = 0;
+    for line in INPUT.lines() {
+        let report = line
+            .split_whitespace()
+            .filter_map(|num| {
+                str::parse::<u8>(num).ok()
+            });
+
+        still_safe += u16::from(is_still_safe(report));
+    }
+
+    println!("Part 2: {}", still_safe);
+}
+
+fn is_safe(mut report: impl Iterator<Item = u8>) -> bool {
+    let mut ascending = true;
+    let mut descending = true;
+    let mut correct_gaps = true;
+    let Some(mut prev) = report.next() else {
+        return true;
+    };
+    while let Some(level) = report.next() {
+        ascending &= prev <= level;
+        descending &= prev >= level;
+        correct_gaps &= matches!(prev.abs_diff(level), 1..=3);
+
+        prev = level;
+    }
+
+    (ascending || descending) && correct_gaps
+}
+
+fn is_still_safe(report: impl Iterator<Item = u8>) -> bool {
+    let report = report.collect::<Vec<_>>();
+    let mut is_still_safe = false;
+    for removal in 0..report.len() {
+        let altered_report = report.iter().copied().enumerate().filter_map(|(idx, level)| {
+            if idx == removal {
+                None
+            } else {
+                Some(level)
+            }
+        });
+
+        is_still_safe |= is_safe(altered_report);
+    };
+    
+    is_still_safe
+}