Implement 2025 - Day 1 - Part 2

2025/01.rs

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+---cargo
+---
+
+static CONTENT: &'static str = include_str!("./inputs/01_1.txt");
+
+#[derive(Debug)]
+enum Direction {
+    Left,
+    Right,
+}
+
+#[derive(Debug)]
+struct Rotation {
+    direction: Direction,
+    amount: usize,
+}
+
+fn main() {
+    let rotations: Vec<Rotation> = CONTENT.lines().map(|l| l.trim()).filter(|l| !l.is_empty()).map(|l| {
+        let (direction, raw_amount) = l.split_at(1);
+
+        let direction = match direction {
+            "L" => Direction::Left,
+            "R" => Direction::Right,
+            other => unreachable!("Unknown Direction: {:?}", other),
+        };
+
+        let amount = match raw_amount.parse::<usize>() {
+            Ok(a) => a,
+            Err(e) => unreachable!("Invalid Amount ({:?}): {:?}", raw_amount, e),
+        };
+
+        Rotation {
+            direction,
+            amount,
+        }
+    }).collect();
+
+    println!("Rotations: {:#?}", rotations);
+
+    let mut count: usize = 0;
+
+    let mut state: isize = 50;
+    for rot in rotations.iter() {
+        if rot.amount >= 100 {
+            count += rot.amount / 100;
+        }
+
+        let amount = rot.amount % 100;
+        if amount == 0 {
+            continue;
+        }
+
+        match rot.direction {
+            Direction::Left => {
+                if state != 0 && amount > state as usize {
+                    count += 1;
+                }
+
+                state = state.strict_sub_unsigned(amount);
+                state = state.strict_rem_euclid(100);
+
+                if state == 0 {
+                    count += 1;
+                }
+            }
+            Direction::Right => {
+                state = state.strict_add_unsigned(amount);
+                if state >= 100 {
+                    count += 1;
+                }
+
+                state = state.strict_rem_euclid(100);
+            }
+        };
+
+        println!("Applying {:?} => {} ({})", rot, state, count);
+    }
+
+    println!("Result: {}", count);
+}

2025/inputs/01_example.txt

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+L68
+L30
+R48
+L5
+R60
+L55
+L1
+L99
+R14
+L82

README.md

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+# Advent of Code