day 12 part 2 look for corners by two blueprints

newday.sh

@@ -0,0 +1,32 @@
+#!/bin/bash
+
+# Check if the correct number of arguments is provided
+if [ "$#" -ne 1 ]; then
+    echo "Usage: $0 <two_digit_number>"
+    exit 1
+fi
+
+# Get the parameters
+X="$1"
+
+# Validate that X is a two-digit number
+if ! [[ "$X" =~ ^[0-9]{2}$ ]]; then
+    echo "Error: The parameter must be a two-digit number."
+    exit 1
+fi
+
+cp src/template.rs src/day$X.rs
+git add src/day$X.rs
+touch input/day$X.txt
+
+# Define the placeholder you want to replace
+PLACEHOLDER="{{day}}"
+
+# Use sed to replace the placeholder with the desired text
+sed -i "s|$PLACEHOLDER|$X|g" "src/day$X.rs"
+sed -i "s/.*\/\/ PLACEHOLDER.*/pub mod day$X;\n\/\/ PLACEHOLDER/" "src/lib.rs"
+sed -i "s/.*\/\/ PLACEHOLDER.*/($X, day$X::day_main),\n\/\/ PLACEHOLDER/" "src/main.rs"
+
+cargo fmt
+
+echo "seems allright. created template for day $X"

src/day05.rs

@@ -108,8 +108,8 @@ mod test {
 
     #[test]
     fn test1() {
-        assert!(valid_book(&vec![97, 5, 13], &HashSet::from([(97, 13)])));
-        assert!(!valid_book(&vec![13, 5, 97], &HashSet::from([(97, 13)])));
+        assert!(valid_book(&[97, 5, 13], &HashSet::from([(97, 13)])));
+        assert!(!valid_book(&[13, 5, 97], &HashSet::from([(97, 13)])));
         assert_eq!(part1(TEST_INPUT), 143);
     }
 

src/day06.rs

@@ -1,7 +1,6 @@
-use std::{
-    collections::{HashMap, HashSet},
-    fs::read_to_string,
-};
+use std::{collections::HashSet, fs::read_to_string};
+
+use crate::utils::grid::{Coord, Grid};
 
 pub fn day_main() {
     let input = read_to_string("input/day06.txt").unwrap();
@@ -11,7 +10,6 @@ pub fn day_main() {
 }
 
 type RiddleResult = usize;
-type Point = (i32, i32);
 
 fn part1(input: &str) -> RiddleResult {
     let (m, pos) = parse(input);
@@ -21,13 +19,9 @@ fn part1(input: &str) -> RiddleResult {
     visited.len()
 }
 
-fn get_visited(
-    m: &HashMap<(i32, i32), char>,
-    mut pos: (i32, i32),
-    mut dir: char,
-) -> HashSet<(i32, i32)> {
+fn get_visited(m: &Grid<char>, mut pos: Coord, mut dir: char) -> HashSet<Coord> {
     let mut visited = HashSet::new();
-    while m.contains_key(&pos) {
+    while m.contains_key(pos) {
         let (x, y) = pos;
         visited.insert(pos);
         let next = match dir {
@@ -37,7 +31,7 @@ fn get_visited(
             '>' => (x + 1, y),
             _ => unreachable!(),
         };
-        if let Some('#') = m.get(&next) {
+        if m.contains_key(next) && '#' == m[next] {
             dir = match dir {
                 '^' => '>',
                 'v' => '<',
@@ -62,25 +56,14 @@ fn part2(input: &str) -> RiddleResult {
         .count()
 }
 
-fn parse(input: &str) -> (HashMap<Point, char>, Point) {
-    let mut m = HashMap::new();
-    let mut pos = None;
-    input.lines().enumerate().for_each(|(y, line)| {
-        line.char_indices().for_each(|(x, c)| {
-            let x = x as i32;
-            let y = y as i32;
-            if c == '^' {
-                pos = Some((x, y));
-                m.insert((x, y), '.');
-            } else {
-                m.insert((x, y), c);
-            }
-        });
-    });
-    (m, pos.unwrap())
+fn parse(input: &str) -> (Grid<char>, Coord) {
+    let mut m = Grid::parse(input);
+    let start = m.entries().find(|(_, c)| **c == '^').unwrap().0;
+    m[start] = '.';
+    (m, start)
 }
 
-fn is_loop(m: &HashMap<Point, char>, block: Point, mut pos: Point, mut dir: char) -> bool {
+fn is_loop(m: &Grid<char>, block: Coord, mut pos: Coord, mut dir: char) -> bool {
     let mut visited = HashSet::new();
     loop {
         let (x, y) = pos;
@@ -92,10 +75,9 @@ fn is_loop(m: &HashMap<Point, char>, block: Point, mut pos: Point, mut dir: char
             '>' => (x + 1, y),
             _ => unreachable!(),
         };
-        let next_tile = m.get(&next);
-        if None == next_tile {
+        if !m.contains_key(next) {
             return false;
-        } else if next == block || Some(&'#') == next_tile {
+        } else if next == block || '#' == m[next] {
             // we only check for loops on a collision to speed things up
             if visited.contains(&(pos, dir)) {
                 return true;

src/day07.rs

@@ -0,0 +1,135 @@
+use std::fs::read_to_string;
+
+use itertools::Itertools;
+use regex::Regex;
+
+pub fn day_main() {
+    let input = read_to_string("input/day07.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = i64;
+
+fn part1(input: &str) -> RiddleResult {
+    let regex = Regex::new("(\\d+)").unwrap();
+    input
+        .lines()
+        .map(|line| {
+            regex
+                .find_iter(line)
+                .map(|capture| capture.as_str().parse::<i64>().unwrap())
+                .collect_vec()
+        })
+        .filter(|v| well_calibrated(v))
+        .map(|v| v[0])
+        .sum()
+}
+
+fn well_calibrated(list: &[i64]) -> bool {
+    let expected = list[0];
+    let operands = list.iter().skip(1).copied().collect_vec();
+    let operators = ops(operands.len() - 1);
+    for ops in operators.into_iter() {
+        let v = ops
+            .into_iter()
+            .zip(operands.iter().skip(1))
+            .fold(operands[0], |acc, (op, val)| match op {
+                '*' => acc * val,
+                '+' => acc + val,
+                _ => panic!(),
+            });
+        if v == expected {
+            return true;
+        }
+    }
+    false
+}
+
+fn ops(n: usize) -> Vec<Vec<char>> {
+    if n == 1 {
+        return vec![vec!['+'], vec!['*']];
+    }
+    let v = ops(n - 1);
+    v.into_iter()
+        .flat_map(|vector| {
+            let mut v1 = vector.clone();
+            let mut v2 = vector;
+            v1.push('+');
+            v2.push('*');
+            [v1, v2]
+        })
+        .collect_vec()
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let regex = Regex::new("(\\d+)").unwrap();
+    input
+        .lines()
+        .map(|line| {
+            regex
+                .find_iter(line)
+                .map(|capture| capture.as_str().parse::<i64>().unwrap())
+                .collect_vec()
+        })
+        .filter(|v| well(v[0], v[1], &v[2..]))
+        .map(|v| v[0])
+        .sum()
+}
+
+fn well(expected: i64, acc: i64, operands: &[i64]) -> bool {
+    if operands.is_empty() {
+        return expected == acc;
+    }
+    if acc > expected {
+        return false;
+    }
+
+    let next = operands[0];
+    let remainder = &operands[1..];
+
+    let v_mul = acc * next;
+    let v_plus = acc + next;
+    let v_concat = concat(acc, next);
+    well(expected, v_mul, remainder)
+        || well(expected, v_plus, remainder)
+        || well(expected, v_concat, remainder)
+}
+
+fn concat(lhs: i64, rhs: i64) -> i64 {
+    let exp: u32 = (rhs as f64 + 1.0).log10().ceil() as u32;
+    let shift = 10i64.pow(exp);
+    lhs * shift + rhs
+}
+
+#[cfg(test)]
+mod test {
+    use super::{concat, part1, part2};
+
+    const TEST_INPUT: &str = r"190: 10 19
+3267: 81 40 27
+83: 17 5
+156: 15 6
+7290: 6 8 6 15
+161011: 16 10 13
+192: 17 8 14
+21037: 9 7 18 13
+292: 11 6 16 20";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 3749);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 11387);
+    }
+
+    #[test]
+    fn test_concat() {
+        assert_eq!(1234, concat(12, 34));
+        assert_eq!(1210, concat(12, 10));
+    }
+}

src/day08.rs

@@ -0,0 +1,107 @@
+use std::{collections::HashSet, fs::read_to_string};
+
+use itertools::Itertools;
+
+use crate::utils::grid::Grid;
+
+pub fn day_main() {
+    let input = read_to_string("input/day08.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    let grid = Grid::parse(input);
+    let mut antinodes = HashSet::new();
+    let antennas = grid
+        .entries()
+        .filter(|(_, c)| **c != '.')
+        .into_group_map_by(|(_, c)| *c);
+    for (_, coords) in antennas {
+        for (a, _) in coords.iter() {
+            for (b, _) in coords.iter() {
+                if a == b {
+                    continue;
+                }
+                let dx = a.0 - b.0;
+                let dy = a.1 - b.1;
+                let p = (a.0 + dx, a.1 + dy);
+                if grid.contains_key(p) {
+                    antinodes.insert(p);
+                }
+            }
+        }
+    }
+    antinodes.len()
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let grid = Grid::parse(input);
+    let mut antinodes = HashSet::new();
+    let antennas = grid
+        .entries()
+        .filter(|(_, c)| **c != '.')
+        .into_group_map_by(|(_, c)| *c);
+    for (_, coords) in antennas {
+        for (a, _) in coords.iter() {
+            for (b, _) in coords.iter() {
+                if a == b {
+                    continue;
+                }
+                antinodes.insert(*a);
+                antinodes.insert(*b);
+                let dx = a.0 - b.0;
+                let dy = a.1 - b.1;
+                for i in 1.. {
+                    let p = (a.0 + i * dx, a.1 + i * dy);
+                    if grid.contains_key(p) {
+                        antinodes.insert(p);
+                    } else {
+                        break;
+                    }
+                }
+                for i in 1.. {
+                    let p = (a.0 - i * dx, a.1 - i * dy);
+                    if grid.contains_key(p) {
+                        antinodes.insert(p);
+                    } else {
+                        break;
+                    }
+                }
+            }
+        }
+    }
+    antinodes.len()
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 14);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 34);
+    }
+}

src/day09.rs

@@ -0,0 +1,116 @@
+use std::fs::read_to_string;
+
+pub fn day_main() {
+    let input = read_to_string("input/day09.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    let mut disk = Vec::with_capacity(input.len() * 10);
+    for (i, l) in input.chars().enumerate() {
+        let l = l.to_digit(10).unwrap();
+        let content = if i % 2 == 0 {
+            // file
+            Some(i / 2) // id based on order of apperance and every second one is a file
+        } else {
+            None
+        };
+        for _ in 0..l {
+            disk.push(content);
+        }
+    }
+    // dbg!(disk);
+    let mut free = disk
+        .iter()
+        .enumerate()
+        .find(|(_, v)| v.is_none())
+        .unwrap()
+        .0;
+    let mut last_block = disk.len() - 1;
+
+    while free < last_block {
+        if disk[free].is_some() {
+            break;
+        }
+        disk[free] = disk[last_block];
+        disk[last_block] = None;
+        while last_block > 0 && disk[last_block].is_none() {
+            last_block -= 1;
+        }
+        while free < disk.len() && disk[free].is_some() {
+            free += 1;
+        }
+    }
+    disk.into_iter()
+        .take(free)
+        .enumerate()
+        .map(|(i, v)| i * v.unwrap())
+        .sum()
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let mut disk = Vec::with_capacity(input.len() * 10);
+    // (start_index, len, file_id)
+    let mut files: Vec<(usize, u32, usize)> = Vec::with_capacity(input.len() / 2 + 1);
+    for (i, l) in input.chars().enumerate() {
+        let l = l.to_digit(10).unwrap();
+        let content = if i % 2 == 0 {
+            // file
+            Some(i / 2) // id based on order of apperance and every second one is a file
+        } else {
+            None
+        };
+        if i % 2 == 0 {
+            files.push((disk.len(), l, i / 2));
+        }
+        for _ in 0..l {
+            disk.push(content);
+        }
+    }
+    while let Some((start_index, length, file_id)) = files.pop() {
+        let mut seeker = 0;
+        let mut found = None;
+        while disk[seeker] != Some(file_id) {
+            if disk[seeker..seeker + length as usize]
+                .iter()
+                .all(|v| v.is_none())
+            {
+                found = Some(seeker);
+                break;
+            }
+            seeker += 1;
+        }
+        if let Some(empty_start) = found {
+            for i in 0..length as usize {
+                disk[empty_start + i] = Some(file_id);
+                disk[start_index + i] = None;
+            }
+        }
+    }
+
+    disk.into_iter()
+        .enumerate()
+        .map(|(i, v)| if let Some(value) = v { i * value } else { 0 })
+        .sum()
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"2333133121414131402";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 1928);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 2858);
+    }
+}

src/day10.rs

@@ -0,0 +1,141 @@
+use std::{
+    collections::{HashMap, HashSet},
+    fs::read_to_string,
+};
+
+use itertools::Itertools;
+
+use crate::utils::grid::Grid;
+
+pub fn day_main() {
+    let input = read_to_string("input/day10.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input)); // 832 wrong
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    solve(input, true)
+}
+
+fn solve(input: &str, visit_once: bool) -> usize {
+    let grid = Grid::parse(input);
+    let m: HashMap<(i64, i64), u32> = HashMap::from_iter(grid.entries().map(|((x, y), c)| {
+        (
+            (x, y),
+            if *c == '.' {
+                1000
+            } else {
+                c.to_digit(10).unwrap()
+            },
+        )
+    }));
+    let grid = Grid::from(m);
+    let trail_heads = grid.entries().filter(|(_, h)| **h == 0).collect_vec();
+    let mut result = 0;
+    for (th, th_height) in trail_heads {
+        let mut count = 0;
+        let mut visited = HashSet::new();
+        let mut queue = vec![(th, th_height)];
+        while let Some((p, h)) = queue.pop() {
+            if visit_once && visited.contains(&(p, h)) {
+                continue;
+            }
+            visited.insert((p, h));
+
+            if *h == 9 {
+                count += 1;
+                continue;
+            }
+
+            let nexts = vec![
+                (p.0, p.1 + 1),
+                (p.0, p.1 - 1),
+                (p.0 + 1, p.1),
+                (p.0 - 1, p.1),
+            ];
+
+            for next in nexts {
+                if let Some(nh) = grid.get(next) {
+                    if *nh == h + 1 {
+                        queue.push((next, nh));
+                    }
+                }
+            }
+        }
+        result += count;
+    }
+    result
+}
+
+fn part2(input: &str) -> RiddleResult {
+    solve(input, false)
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 36);
+    }
+    #[test]
+    fn test1a() {
+        assert_eq!(
+            part1(
+                r"0123
+1234
+8765
+9876
+"
+            ),
+            1
+        );
+    }
+
+    #[test]
+    fn test1b() {
+        assert_eq!(
+            part1(
+                r"...0...
+...1...
+...2...
+6543456
+7.....7
+8.....8
+9.....9
+"
+            ),
+            2
+        );
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(
+            part2(
+                r".....0.
+..4321.
+..5..2.
+..6543.
+..7..4.
+..8765.
+..9....
+"
+            ),
+            3
+        );
+    }
+}

src/day11.rs

@@ -0,0 +1,56 @@
+use std::{collections::HashMap, fs::read_to_string};
+
+pub fn day_main() {
+    let input = read_to_string("input/day11.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    solve(input, 25)
+}
+
+fn solve(input: &str, blinks: i32) -> usize {
+    let mut stones: HashMap<usize, usize> =
+        input.split(" ").map(|v| (v.parse().unwrap(), 1)).collect();
+    let mut next = HashMap::new();
+    for _ in 0..blinks {
+        for (k, v) in stones {
+            if k == 0 {
+                next.entry(1).and_modify(|count| *count += v).or_insert(v);
+            } else if (k.ilog10() + 1) % 2 == 0 {
+                let l = (k.ilog10() + 1) / 2;
+                let z: usize = 10usize.pow(l);
+                let a = k / z;
+                let b = k % z;
+                next.entry(a).and_modify(|count| *count += v).or_insert(v);
+                next.entry(b).and_modify(|count| *count += v).or_insert(v);
+            } else {
+                let k_new = k * 2024;
+                next.entry(k_new)
+                    .and_modify(|count| *count += v)
+                    .or_insert(v);
+            }
+        }
+        stones = next;
+        next = HashMap::new();
+    }
+    stones.values().to_owned().sum()
+}
+
+fn part2(input: &str) -> RiddleResult {
+    solve(input, 75)
+}
+
+#[cfg(test)]
+mod test {
+    use super::part1;
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1("125 17"), 55312);
+    }
+}

src/day12.rs

@@ -0,0 +1,113 @@
+use std::{collections::HashSet, fs::read_to_string};
+
+use itertools::Itertools;
+
+use crate::utils::grid::{Coord, Grid};
+
+pub fn day_main() {
+    let input = read_to_string("input/day12.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = u64;
+
+const NEIGHBORS: &[Coord] = &[(1, 0), (0, 1), (-1, 0), (0, -1)];
+
+fn part1(input: &str) -> RiddleResult {
+    let garden = Grid::parse(input);
+    let mut processed: HashSet<Coord> = HashSet::new();
+    let mut result = 0;
+    for (p, c) in garden.entries() {
+        if processed.contains(&p) {
+            continue;
+        }
+        let mut area = 0;
+        let mut fence = 0;
+        let mut further = vec![p];
+        while let Some(current) = further.pop() {
+            if processed.contains(&current) {
+                continue;
+            }
+            area += 1;
+            for next in NEIGHBORS.iter().map(|d| (current.0 + d.0, current.1 + d.1)) {
+                let next_c = garden.get(next);
+                if next_c.is_none() || next_c.unwrap() != c {
+                    fence += 1;
+                } else {
+                    further.push(next);
+                }
+            }
+            processed.insert(current);
+        }
+        result += area * fence;
+    }
+    result
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let garden = Grid::parse(input);
+    let mut processed: HashSet<Coord> = HashSet::new();
+    let mut result = 0;
+    for (p, c) in garden.entries() {
+        if processed.contains(&p) {
+            continue;
+        }
+        let mut area = 0;
+        let mut further = vec![p];
+        let mut convex_corners = 0;
+        let mut concave_corners = 0;
+        while let Some(current) = further.pop() {
+            if processed.contains(&current) {
+                continue;
+            }
+            area += 1;
+            for next in NEIGHBORS.iter().map(|d| (current.0 + d.0, current.1 + d.1)) {
+                let next_c = garden.get(next);
+                if next_c.is_none() || next_c.unwrap() != c {
+                } else {
+                    further.push(next);
+                }
+            }
+            processed.insert(current);
+            for (da, db) in NEIGHBORS.iter().circular_tuple_windows() {
+                let a = (current.0 + da.0, current.1 + da.1);
+                let b = (current.0 + db.0, current.1 + db.1);
+                if garden.get(a) != Some(c) && garden.get(b) != Some(c) {
+                    convex_corners += 1;
+                } else if garden.get(a) == Some(c)
+                    && garden.get(b) == Some(c)
+                    && garden.get((current.0 + da.0 + db.0, current.1 + da.1 + db.1)) != Some(c)
+                {
+                    concave_corners += 1;
+                }
+            }
+        }
+        let var_name = convex_corners + concave_corners;
+        let var_name = area * (var_name);
+        result += var_name;
+    }
+    result
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"AAAA
+BBCD
+BBCC
+EEEC
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 140);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 80);
+    }
+}

src/lib.rs

@@ -4,3 +4,11 @@ pub mod day03;
 pub mod day04;
 pub mod day05;
 pub mod day06;
+pub mod day07;
+pub mod day08;
+pub mod day09;
+pub mod day10;
+pub mod day11;
+pub mod day12;
+// PLACEHOLDER
+pub mod utils;

src/main.rs

@@ -11,6 +11,13 @@ fn main() {
         (4, day04::day_main),
         (5, day05::day_main),
         (6, day06::day_main),
+        (7, day07::day_main),
+        (8, day08::day_main),
+        (9, day09::day_main),
+        (10, day10::day_main),
+        (11, day11::day_main),
+        (12, day12::day_main),
+        // PLACEHOLDER
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());
     let Some(day) = day else {

src/template.rs

@@ -1,7 +1,7 @@
 use std::fs::read_to_string;
 
 pub fn day_main() {
-    let input = read_to_string("input/dayXX.txt").unwrap();
+    let input = read_to_string("input/day{{day}}.txt").unwrap();
     let input = input.trim();
     println!(" part1: {}", part1(input));
     println!(" part2: {}", part2(input));

src/utils/grid.rs

@@ -0,0 +1,230 @@
+use std::{
+    collections::HashMap,
+    ops::{Index, IndexMut},
+};
+
+use itertools::Itertools;
+
+/// A grid structure, indexed by (x, y) tuples. The top-left coordinate is (0, 0).
+#[derive(Eq, PartialEq, Debug, Clone)]
+pub struct Grid<T> {
+    pub content_width: i64,
+    pub content_height: i64,
+    content: Vec<T>,
+}
+
+pub type Coord = (i64, i64);
+
+impl<T> Grid<T> {
+    pub fn from(mut source: HashMap<Coord, T>) -> Grid<T> {
+        let x_max = source.keys().max_by_key(|c| c.0).unwrap().0;
+        let y_max = source.keys().max_by_key(|c| c.1).unwrap().1;
+        let content_width = x_max + 1;
+        let content_height = y_max + 1;
+        let mut content = Vec::with_capacity((content_width * content_height) as usize);
+        for y in 0..content_height {
+            for x in 0..content_width {
+                let v = source
+                    .remove(&(x, y))
+                    .unwrap_or_else(|| panic!("no entry for {x}, {y}"));
+                content.push(v);
+            }
+        }
+        Grid {
+            content_width,
+            content_height,
+            content,
+        }
+    }
+
+    fn index_of(&self, c: Coord) -> usize {
+        if !self.contains_key(c) {
+            panic!(
+                "point {c:?} out of range (width: {}, height: {})",
+                self.content_width, self.content_height
+            );
+        }
+        (c.1 * self.content_width + c.0) as usize
+    }
+
+    pub fn get(&self, c: Coord) -> Option<&T> {
+        if !self.contains_key(c) {
+            return None;
+        }
+        let index = self.index_of(c);
+        if index < self.content.len() {
+            Some(&self.content[self.index_of(c)])
+        } else {
+            None
+        }
+    }
+
+    pub fn get_mut(&mut self, c: Coord) -> Option<&mut T> {
+        if !self.contains_key(c) {
+            return None;
+        }
+        let index = self.index_of(c);
+        if index < self.content.len() {
+            Some(&mut self.content[index])
+        } else {
+            None
+        }
+    }
+
+    pub fn set(&mut self, c: Coord, value: T) {
+        let index_of = self.index_of(c);
+        self.content[index_of] = value;
+    }
+
+    pub fn contains_key(&self, c: Coord) -> bool {
+        0 <= c.0 && c.0 < self.content_width && 0 <= c.1 && c.1 < self.content_height
+    }
+
+    pub fn entries(&self) -> impl Iterator<Item = (Coord, &T)> {
+        self.content.iter().enumerate().map(|(i, val)| {
+            (
+                (i as i64 % self.content_width, i as i64 / self.content_width),
+                val,
+            )
+        })
+    }
+
+    pub fn map_values<U>(self, f: fn(T) -> U) -> Grid<U> {
+        let new_content = self.content.into_iter().map(f).collect_vec();
+        Grid {
+            content_width: self.content_width,
+            content_height: self.content_height,
+            content: new_content,
+        }
+    }
+}
+
+impl Grid<char> {
+    pub fn parse(input: &str) -> Grid<char> {
+        let content_width = input.lines().next().unwrap().len();
+        let mut content_height = 0;
+        let mut content = vec![];
+        for line in input.lines() {
+            content_height += 1;
+            content.reserve(content_width);
+            line.chars().for_each(|v| content.push(v));
+        }
+        Grid {
+            content_width: content_width as i64,
+            content_height,
+            content,
+        }
+    }
+}
+
+impl<T> Index<Coord> for Grid<T> {
+    type Output = T;
+
+    #[inline]
+    fn index(&self, index: Coord) -> &Self::Output {
+        &self.content[self.index_of(index)]
+    }
+}
+
+impl<T> IndexMut<Coord> for Grid<T> {
+    fn index_mut(&mut self, index: Coord) -> &mut Self::Output {
+        let index_of = self.index_of(index);
+        &mut self.content[index_of]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use itertools::Itertools;
+
+    use super::Grid;
+    use std::collections::HashMap;
+
+    #[test]
+    fn init_and_read() {
+        let grid: Grid<char> = Grid::from(HashMap::from_iter([
+            ((0, 0), '.'),
+            ((0, 1), '.'),
+            ((1, 0), '.'),
+            ((1, 1), '#'),
+        ]));
+        assert_eq!('.', grid[(0, 0)]);
+        assert_eq!('.', grid[(0, 1)]);
+        assert_eq!('.', grid[(1, 0)]);
+        assert_eq!('#', grid[(1, 1)]);
+    }
+
+    #[test]
+    fn mutate_by_index() {
+        let mut grid = generate();
+        grid[(0, 1)] = 'x';
+        assert_eq!('x', grid[(0, 1)]);
+    }
+    #[test]
+    fn mutate_option() {
+        let mut grid = generate();
+        if let Some(value) = grid.get_mut((0, 1)) {
+            *value = 'x';
+        }
+        assert_eq!('x', grid[(0, 1)]);
+    }
+
+    fn generate() -> Grid<char> {
+        let grid: Grid<char> = Grid::from(HashMap::from_iter([
+            ((0, 0), '.'),
+            ((0, 1), '.'),
+            ((1, 0), '.'),
+            ((1, 1), '.'),
+        ]));
+        grid
+    }
+
+    #[test]
+    fn from_str() {
+        let s = "..\n.x";
+        let m_str = Grid::parse(s);
+        let mut m_gen = generate();
+        m_gen[(1, 1)] = 'x';
+        assert_eq!(m_gen, m_str);
+    }
+
+    #[test]
+    fn entries() {
+        let v = vec![
+            ((0, 0), &'.'),
+            ((1, 0), &'.'),
+            ((0, 1), &'.'),
+            ((1, 1), &'.'),
+        ];
+        assert_eq!(v, generate().entries().collect_vec());
+    }
+
+    #[should_panic]
+    #[test]
+    fn out_of_bounds_panics1() {
+        generate()[(-1, 3)];
+    }
+
+    #[should_panic]
+    #[test]
+    fn out_of_bounds_panics2() {
+        generate()[(1, 3)];
+    }
+
+    #[test]
+    fn option_success() {
+        assert_eq!(Some(&'.'), generate().get((0, 0)));
+    }
+
+    #[test]
+    fn option_out_of_bounds() {
+        assert_eq!(None, generate().get((30, 0)));
+    }
+
+    #[test]
+    fn value_mapping() {
+        let a: Grid<char> = generate();
+        let b: Grid<String> = a.map_values(|old| format!("{old}string"));
+        assert_eq!(".string".to_string(), b[(0, 0)]);
+    }
+}

src/utils/mod.rs

@@ -0,0 +1 @@
+pub mod grid;