RussellChamp/advent-of-code-2025-cursor
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Refactor days 1-2, optimize day 3 part 1 with suffix max

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Russell Champoux committed 2025-12-04 17:34:11 -05:00
1 parent 0b5c8fa10f
commit d650dce61b
6 files changed
+133 -149
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src/bin/01.rs
+63 -70
View File
@@ -1,81 +1,74 @@
advent_of_code::solution!(1);
pub fn part_one(input: &str) -> Option<u64> {
let mut position: i32 = 50;
let mut count = 0u64;
for line in input.lines() {
let line = line.trim();
if line.is_empty() {
continue;
}
let direction = &line[0..1];
let distance: i32 = line[1..].parse().ok()?;
match direction {
"L" => position = (position - distance).rem_euclid(100),
"R" => position = (position + distance).rem_euclid(100),
_ => return None,
}
if position == 0 {
count += 1;
}
/// Parse a rotation instruction like "L68" or "R14" into (direction, distance)
fn parse_rotation(line: &str) -> Option<(char, i32)> {
let line = line.trim();
if line.is_empty() {
return None;
}
let direction = line.chars().next()?;
let distance: i32 = line[1..].parse().ok()?;
Some((direction, distance))
}
/// Apply a rotation and return the new position
fn apply_rotation(position: i32, direction: char, distance: i32) -> i32 {
match direction {
'L' => (position - distance).rem_euclid(100),
'R' => (position + distance).rem_euclid(100),
_ => position,
}
}
/// Count how many times we pass through 0 during a rotation
fn count_zeros(position: i32, direction: char, distance: i32) -> i32 {
match direction {
'L' => {
if position == 0 {
distance / 100
} else if distance >= position {
(distance - position) / 100 + 1
} else {
0
}
}
'R' => {
if position == 0 {
distance / 100
} else if distance >= 100 - position {
(distance + position - 100) / 100 + 1
} else {
0
}
}
_ => 0,
}
}
pub fn part_one(input: &str) -> Option<u64> {
let count = input
.lines()
.filter_map(parse_rotation)
.fold((50i32, 0u64), |(pos, count), (dir, dist)| {
let new_pos = apply_rotation(pos, dir, dist);
let new_count = count + if new_pos == 0 { 1 } else { 0 };
(new_pos, new_count)
})
.1;
Some(count)
}
pub fn part_two(input: &str) -> Option<u64> {
let mut position: i32 = 50;
let mut count = 0u64;
for line in input.lines() {
let line = line.trim();
if line.is_empty() {
continue;
}
let direction = &line[0..1];
let distance: i32 = line[1..].parse().ok()?;
// Count how many times we pass through 0 during this rotation
let zeros = match direction {
"L" => {
// Moving left: we hit 0 at clicks p, p+100, p+200, ... (if p > 0)
// or at clicks 100, 200, 300, ... (if p = 0)
if position == 0 {
distance / 100
} else if distance >= position {
(distance - position) / 100 + 1
} else {
0
}
}
"R" => {
// Moving right: we hit 0 at click (100-p), then (100-p)+100, etc.
// or at clicks 100, 200, 300, ... (if p = 0)
if position == 0 {
distance / 100
} else if distance >= 100 - position {
(distance + position - 100) / 100 + 1
} else {
0
}
}
_ => return None,
};
count += zeros as u64;
// Update position
match direction {
"L" => position = (position - distance).rem_euclid(100),
"R" => position = (position + distance).rem_euclid(100),
_ => {}
}
}
let count = input
.lines()
.filter_map(parse_rotation)
.fold((50i32, 0u64), |(pos, count), (dir, dist)| {
let zeros = count_zeros(pos, dir, dist) as u64;
let new_pos = apply_rotation(pos, dir, dist);
(new_pos, count + zeros)
})
.1;
Some(count)
}