diff --git a/day19/src/main.rs b/day19/src/main.rs
index 0957e3b..25008e8 100644
--- a/day19/src/main.rs
+++ b/day19/src/main.rs
@@ -1,8 +1,23 @@
+use std::collections::HashSet;
 use std::collections::HashMap;
 use std::env;
 use std::fs;
 
-use regex::Regex;
+use crate::Dir::{North, South, East, West };
+
+
+type Coord = (i32, i32);
+#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug, PartialOrd, Ord)]
+enum Dir { North, South, East, West }
+
+fn step(start: &Coord, d: Dir, steps: i32) -> Coord {
+    match d {
+        North => (start.0, start.1 - steps),
+        South => (start.0, start.1 + steps),
+        East => (start.0 + steps, start.1),
+        West => (start.0 - steps, start.1),
+    }
+}
 
 fn main() {
     println!("Hello, AoC day 13!");
@@ -18,109 +33,69 @@ fn main() {
     let binding = fs::read_to_string(file_path)
         .expect("should be able to read the file");
 
-    let (towels, designs) = binding.split_once("\n\n").expect("should have two sections");
+    let mut map = HashMap::new();
+    let mut distances_to_end: HashMap<Coord, i32> = HashMap::new();
 
-    let all_towels: Vec<&str> = towels.split(", ").collect();
-
-    let re = Regex::new(
-            &format!("^({})+$", all_towels.join("|"))
-        ).expect("making the regex");
-    
-    let mut count = 0;
-    for line in designs.lines() {
-        if re.is_match(line) {
-            count += 1;
+    let mut start = (0,0);
+    let mut exit = (0,0);
+    let mut y = 0;
+    for line in binding.lines() {
+        let mut x = 0;
+        for c in line.chars() {
+            match c {
+                'S' => { start = (x,y); map.insert((x,y), '.'); },
+                'E' => { exit = (x,y); map.insert((x,y), '.'); },
+                _ => { map.insert((x,y), c); }
+            };
+            x += 1;
         }
+        y += 1;
     }
 
-    println!("found {count} valid designs");
+    distances_to_end.insert(exit, 0);
+    let visited: HashSet<Coord> = HashSet::new();
+    let mut wavefront: Vec<Coord> = vec![exit];
+    while let Some(here) = wavefront.pop() {
+        let here_distance = distances_to_end.get(&here).unwrap().clone();
+        for x in neighbors(&here) {
+            if map.get(&x) != Some(&'.') {
+                continue;
+            }
+            if visited.contains(&x) {
+                continue;
+            }
+            if let Some(d) = distances_to_end.get(&x) {
+                if *d < here_distance {
+                    continue;
+                }
+            }
+            distances_to_end.insert(x, here_distance + 1);
+            wavefront.push(x);
+        }
 
-    let mut tree = build_tree(&all_towels);
-
-    //println!("{tree:?}");
-    println!("{} nodes in the tree", tree.len());
-
-    let mut count = 0;
-
-    for line in designs.lines() {
-        count += eat(&mut tree, line);
     }
 
-    println!("found {count} solutions total");
+    println!("the distance from {start:?} to {exit:?} is {}", distances_to_end.get(&start).unwrap());
+
 }
 
-fn eat(tree: &mut Vec<TreeCell>, haystack: &str) -> u128 {
-    let mut heads: HashMap<usize, u128> = HashMap::new();
-    heads.insert(0, 1);
-
-    //println!("examining {haystack}");
-
-    for c in haystack.chars() {
-        // iterating by character
-        let mut new_heads = HashMap::new();
-
-        //println!("looking at {c}; the heads we're tracking are {heads:?}");
-
-        // this first loop branches to the start from valid states
-        for (node_idx, num_heads) in heads.drain() {
-            let TreeCell { next: _, valid } = &tree[node_idx];
-            if *valid {
-                let next_idx = 0;
-                let existing_heads = new_heads.get(&next_idx).unwrap_or(&0);
-                new_heads.insert(next_idx, existing_heads + num_heads);
-            }
-            let existing_heads = new_heads.get(&node_idx).unwrap_or(&0);
-            new_heads.insert(node_idx, existing_heads + num_heads);
-        }
-
-        // this second loop advances all the heads
-        for (node_idx, num_heads) in new_heads.drain() {
-            let TreeCell { next, valid: _ } = &tree[node_idx];
-            if let Some(next_idx) = next.get(&c) {
-                heads.insert(*next_idx, num_heads);
-            }
-        }
-    }
-
-    let mut count = 0;
-    
-    for (node_idx, number) in heads {
-        if tree[node_idx].valid { count += number; }
-    }
-    //println!("there are {count} heads in success states");
-
-    return count;
+fn second_neighbors(start: &Coord) -> Vec<Coord> {
+    vec![
+        step(start, North, 2),
+        step(&step(start, North, 1), West, 1),
+        step(&step(start, North, 1), East, 1),
+        step(start, West, 2),
+        step(start, East, 2),
+        step(&step(start, West, 1), South, 1),
+        step(&step(start, East, 1), South, 1),
+        step(start, South, 2)
+    ]
 }
-
-
-#[derive(PartialEq, Eq, Clone, Debug)]
-struct TreeCell {next: HashMap<char, usize>, valid: bool}
-
-fn build_tree(patterns: &[&str]) -> Vec<TreeCell> {
-    let mut cells = vec![TreeCell {next: HashMap::new(), valid: false}];
-
-    for stripes in patterns {
-        add_to_tree(stripes, &mut cells, 0);
-    }
-
-    return cells;
-}
-
-fn add_to_tree(pattern: &str, tree: &mut Vec<TreeCell>, index: usize) {
-    match pattern.chars().next() {
-        None => tree[index].valid = true,
-        Some(c) => {
-            if tree[index].next.contains_key(&c) {
-                add_to_tree(&pattern[1..], tree, *tree[index].next.get(&c).unwrap());
-            } else {
-                let new_index = tree.len();
-                let new_treecell = TreeCell { next: HashMap::new(), valid: false };
-                tree.push(new_treecell); // now this is at new_index
-                tree[index].next.insert(c, new_index);
-                
-                add_to_tree(&pattern[1..], tree, new_index);
-
-            }
-        }
-    }
+fn neighbors(start: &Coord) -> Vec<Coord> {
+    vec![
+        step(start, North, 1),
+        step(start, West, 1),
+        step(start, East, 1),
+        step(start, South, 1)
+    ]
 }
\ No newline at end of file
diff --git a/day20/Cargo.toml b/day20/Cargo.toml
new file mode 100644
index 0000000..156d38d
--- /dev/null
+++ b/day20/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day20"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day20/src/main.rs b/day20/src/main.rs
new file mode 100644
index 0000000..de668e1
--- /dev/null
+++ b/day20/src/main.rs
@@ -0,0 +1,183 @@
+use std::collections::HashSet;
+use std::collections::HashMap;
+use std::env;
+use std::fs;
+
+use crate::Dir::{North, South, East, West };
+
+
+type Coord = (i32, i32);
+#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug, PartialOrd, Ord)]
+enum Dir { North, South, East, West }
+
+fn step(start: &Coord, d: Dir, steps: i32) -> Coord {
+    match d {
+        North => (start.0, start.1 - steps),
+        South => (start.0, start.1 + steps),
+        East => (start.0 + steps, start.1),
+        West => (start.0 - steps, start.1),
+    }
+}
+
+fn main() {
+    println!("Hello, AoC day 13!");
+
+    let args: Vec<String> = env::args().collect();
+    if args.len() != 2 {
+        println!("wrong number of arguments!");
+        std::process::exit(1);
+    }
+
+    let file_path = &args[1];
+
+    let binding = fs::read_to_string(file_path)
+        .expect("should be able to read the file");
+
+    let mut map = HashMap::new();
+
+    let mut start = (0,0);
+    let mut exit = (0,0);
+    let mut y = 0;
+    for line in binding.lines() {
+        let mut x = 0;
+        for c in line.chars() {
+            match c {
+                'S' => { start = (x,y); map.insert((x,y), '.'); },
+                'E' => { exit = (x,y); map.insert((x,y), '.'); },
+                _ => { map.insert((x,y), c); }
+            };
+            x += 1;
+        }
+        y += 1;
+    }
+
+    let mut distances_to_end: HashMap<Coord, i32> = HashMap::new();
+    distances_to_end.insert(exit, 0);
+    let mut visited: HashSet<Coord> = HashSet::new();
+    let mut wavefront: Vec<Coord> = vec![exit];
+    while let Some(here) = wavefront.pop() {
+        let here_distance = distances_to_end.get(&here).unwrap().clone();
+        for x in neighbors(&here) {
+            if map.get(&x) != Some(&'.') {
+                continue;
+            }
+            if visited.contains(&x) {
+                continue;
+            }
+            if let Some(d) = distances_to_end.get(&x) {
+                if *d < here_distance {
+                    continue;
+                }
+            }
+            distances_to_end.insert(x, here_distance + 1);
+            wavefront.push(x);
+        }
+        visited.insert(here);
+    }
+
+    println!("the distance from {start:?} to {exit:?} is {}", distances_to_end.get(&start).unwrap());
+
+    let mut cheats: HashMap<(Coord, Coord), i32> = HashMap::new();
+
+    for (here, distance) in &distances_to_end {
+        for there in second_neighbors(&here) {
+            if let Some(next_distance) = distances_to_end.get(&there) {
+                cheats.insert((*here, there), distance-next_distance);
+            }
+        }
+    }
+
+    let mut counts: HashMap<i32, i32> = HashMap::new();
+
+    for (_, advantage) in cheats {
+        counts.insert(advantage, counts.get(&advantage).unwrap_or(&0) + 1);
+    }
+
+    let mut count = 0;
+    for (x, c) in counts {
+        if x > 100 {
+            count += c;
+        }
+    }
+
+    println!("there were {count} cheats worth more than 100");
+
+    // part b
+
+    let mut cheats: HashMap<(Coord, Coord), i32> = HashMap::new();
+
+    for (here, distance) in &distances_to_end {
+        for there in twenty_step_neighbors(&here) {
+            if let Some(next_distance) = distances_to_end.get(&there) {
+                let cheat_length = (here.0 - there.0).abs() + (here.1 - there.1).abs();
+                cheats.insert((*here, there), distance-next_distance - cheat_length);
+            }
+        }
+    }
+
+    let mut counts: HashMap<i32, i32> = HashMap::new();
+
+    for (_, advantage) in cheats {
+        counts.insert(advantage, counts.get(&advantage).unwrap_or(&0) + 1);
+    }
+
+    let mut count = 0;
+    for (x, c) in counts {
+        if x >= 100 {
+            count += c;
+        }
+    }
+
+    println!("there were {count} cheats worth more than 100");
+}
+
+fn build_cheat_offsets() -> Vec<Coord> {
+    let mut all = vec![(0,0)];
+
+    for _ in 0..20 {
+        all = all.into_iter().flat_map(|x| neighbors(&x)).collect();
+    }
+
+    return all
+}
+
+fn offset_neighbors(start: &Coord, offsets: &Vec<Coord>) -> Vec<Coord> {
+    let mut v: Vec<Coord> = offsets.clone();
+    for x in v.iter_mut() {
+        x.0 = x.0 + start.0;
+        x.1 = x.1 + start.1;
+    }
+    return v;
+}
+
+fn twenty_step_neighbors(start: &Coord) -> Vec<Coord> {
+    let mut v: Vec<Coord> = Vec::with_capacity(400);
+    for x in -20_i32..21 {
+        for y in -20_i32..21 {
+            if x.abs()+y.abs() <= 20 {
+                v.push(step(&step(start, North, y), East, x));
+            }
+        }
+    }
+    return v;
+}
+fn second_neighbors(start: &Coord) -> Vec<Coord> {
+    vec![
+        step(start, North, 2),
+        step(&step(start, North, 1), West, 1),
+        step(&step(start, North, 1), East, 1),
+        step(start, West, 2),
+        step(start, East, 2),
+        step(&step(start, West, 1), South, 1),
+        step(&step(start, East, 1), South, 1),
+        step(start, South, 2)
+    ]
+}
+fn neighbors(start: &Coord) -> Vec<Coord> {
+    vec![
+        step(start, North, 1),
+        step(start, West, 1),
+        step(start, East, 1),
+        step(start, South, 1)
+    ]
+}
\ No newline at end of file
diff --git a/day21/Cargo.toml b/day21/Cargo.toml
new file mode 100644
index 0000000..ed0c318
--- /dev/null
+++ b/day21/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day21"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day21/src/main.rs b/day21/src/main.rs
new file mode 100644
index 0000000..bdd9fb5
--- /dev/null
+++ b/day21/src/main.rs
@@ -0,0 +1,349 @@
+use std::collections::HashSet;
+use std::collections::HashMap;
+use std::env;
+use std::fs;
+
+use crate::Dir::{North, South, East, West, Stay };
+
+
+type Coord = (i32, i32);
+#[derive(Clone, Copy, Eq, PartialEq, Hash, Debug, PartialOrd, Ord)]
+enum Dir { North, South, East, West, Stay }
+
+fn step(start: &Coord, d: Dir, steps: i32) -> Coord {
+    match d {
+        North => (start.0, start.1 - steps),
+        South => (start.0, start.1 + steps),
+        East => (start.0 + steps, start.1),
+        West => (start.0 - steps, start.1),
+        Stay => *start,
+    }
+}
+
+fn walk_path(start: &Coord, path: &[Dir]) -> Coord {
+    let mut here = *start;
+    for d in path {
+        here = step(&here, *d, 1);
+    }
+    return here;
+}
+
+fn main() {
+    println!("Hello, AoC day 21!");
+
+    let args: Vec<String> = env::args().collect();
+    if args.len() != 2 {
+        println!("wrong number of arguments!");
+        std::process::exit(1);
+    }
+
+    let file_path = &args[1];
+
+    let file = fs::read_to_string(file_path)
+        .expect("should be able to read the file");
+
+    let keypad_door: HashMap<char, Coord> = HashMap::from([
+        ('7', (0,0)), ('8', (1,0)), ('9', (2,0)),
+        ('4', (0,1)), ('5', (1,1)), ('6', (2,1)),
+        ('1', (0,2)), ('2', (1,2)), ('3', (2,2)),
+        ('0', (1,3)), ('A', (2,3)),
+        ]);
+    let mut door_map: HashMap<Coord, char> = HashMap::new();
+    for (key, loc) in &keypad_door { door_map.insert(*loc, *key); }
+    let mut directions_matrix: HashMap<(Coord, Coord), Vec<(Dir, i32)>> = HashMap::new();
+    for (_this, here) in &keypad_door {
+        for (_other, there) in &keypad_door {
+            let mut v = vec![];
+            if there.0 > here.0 {
+                v.push((East, there.0 - here.0));
+            }
+            if there.0 < here.0 {
+                v.push((West, here.0 - there.0));
+            }
+            if there.1 > here.1 {
+                v.push((South, there.1 - here.1));
+            }
+            if there.1 < here.1 {
+                v.push((North, here.1 - there.1));
+            }
+            if there == here {
+                v.push((Stay, 0));
+            }
+            directions_matrix.insert((*here, *there), v);
+        }
+    }
+
+
+    let keypad_arrows: HashMap<Dir, Coord> = HashMap::from([
+        (North, (1,0)), (Stay, (2,0)),
+        (West, (0,1)), (South, (1,1)), (East, (2,1)),
+        ]);
+    let mut keypad_map: HashMap<Coord, Dir> = HashMap::new();
+    for (key, loc) in &keypad_arrows { keypad_map.insert(*loc, *key); }
+    let mut keypad_directions_matrix = HashMap::new();
+    for (_this, here) in &keypad_arrows {
+        for (_other, there) in &keypad_arrows {
+            let mut v = vec![];
+            if there.0 > here.0 {
+                v.push((East, there.0 - here.0));
+            }
+            if there.0 < here.0 {
+                v.push((West, here.0 - there.0));
+            }
+            if there.1 > here.1 {
+                v.push((South, there.1 - here.1));
+            }
+            if there.1 < here.1 {
+                v.push((North, here.1 - there.1));
+            }
+            if there == here {
+                v.push((Stay, 0));
+            }
+            keypad_directions_matrix.insert((*here, *there), v);
+        }
+    }
+
+    let mut sum = 0;
+    for line in file.lines() {
+        let door_code: Vec<char> = line.chars().collect();
+        let num: i32 = line[..line.len()-1].parse().expect("failed to parse door code as number");
+        let mut complexity: i64 = 100000000000;
+        
+        for x in &door_code {
+            print!("{}", x);
+        }
+        print!("\n");
+
+        let options_door = build_options(
+            &directions_matrix, 
+            &keypad_door, 
+            &door_code, 
+            'A');
+        for arrow_code_1 in shortest_sequences(options_door, &door_map, keypad_door[&'A']) {
+            print_code(&arrow_code_1);
+
+            let options_arrow_1 = build_options(
+                &keypad_directions_matrix,
+                &keypad_arrows,
+                &arrow_code_1,
+                Stay);
+            for arrow_code_2 in shortest_sequences(options_arrow_1, &keypad_map, keypad_arrows[&Stay]) {
+                print_code(&arrow_code_2);
+
+                let options_arrow_2 = build_options(
+                    &keypad_directions_matrix,
+                    &keypad_arrows,
+                    &arrow_code_2,
+                    Stay);
+                for arrow_code_3 in shortest_sequences(options_arrow_2, &keypad_map, keypad_arrows[&Stay]) {
+                    complexity = complexity.min(arrow_code_3.len() as i64);
+                    print_code(&arrow_code_3);
+                }
+            }
+        }
+        println!("shortest sequence is {} long", complexity);
+        sum += complexity * (num as i64);
+    }
+
+    println!("the sum of the complexity scores is {}", sum);
+
+    // println!("printing out the anomalous code");
+
+    // let code = "<<vAA>A>^AAvA<^A>AvA^A<<vA>>^AAvA^A<vA>^AA<A>A<<vA>A>^AAAvA<^A>A";
+    // let code_dirs = code.chars().map(|x| match x {
+    //     '<' => West, '>' => East, '^' => North, 'v' => South, 'A' => Stay, _ => panic!()
+    // }).collect();
+    // print_code(&code_dirs);
+    // println!("resulting keypresses:");
+    // let code_2 = execute_code(&code_dirs, &keypad_map, keypad_arrows[&Stay]);
+    // print_code(&code_2);
+    // println!("resulting keypresses:");
+    // let code_3 = execute_code(&code_2, &keypad_map, keypad_arrows[&Stay]);
+    // print_code(&code_3);
+    // println!("resulting in:");
+    // let code_4 = execute_code(&code_3, &door_map, keypad_door[&'A']);
+    // print_code_door(&code_4);
+
+
+}
+
+fn first_sequence<T>(options: Vec<Vec<(Dir, i32)>>, map: &HashMap<Coord, T>, start: Coord) -> Vec<Dir> {
+    let mut out = vec![];
+    let mut here = start;
+
+    for choices in options {
+        if choices.len() == 1 {
+            let (direction, times) = choices[0];
+            for _ in 0..times {
+                out.push(direction);
+            }
+            here = step(&here, direction, times)
+        } else if choices.len() == 2 {
+            let (d1, t1) = choices[0];
+            let (d2, t2) = choices[1];
+            if map.contains_key(&step(&here, d1, t1)) {
+                for _ in 0..t1 {
+                    out.push(d1);
+                }
+                
+                for _ in 0..t2 {
+                    out.push(d2);
+                }
+            } else {
+                for _ in 0..t2 {
+                    out.push(d2);
+                }
+
+                for _ in 0..t1 {
+                    out.push(d1);
+                }
+            }
+            
+            
+        }
+    }
+    return out;
+}
+fn sequences<T>(options: Vec<Vec<(Dir, i32)>>, map: &HashMap<Coord, T>, start: Coord) -> Vec<Vec<Dir>> {
+    let mut out: Vec<(Vec<Dir>, Coord)> = vec![(vec![], start)];
+
+    for choices in options {
+        let mut new_out = vec![];
+
+        if choices.len() == 1 {
+            let (direction, times) = choices[0];
+            for (mut walk, mut here) in out {
+                for _ in 0..times {
+                    walk.push(direction);
+                    here = step(&here, direction, 1);
+                }
+                new_out.push((walk, here));
+            }
+        }
+        
+        else if choices.len() == 2 {
+            let (d1, t1) = choices[0];
+            let (d2, t2) = choices[1];
+
+            for (ref walk, here) in &mut out {
+                let end = step(&step(&here, d1, t1), d2, t2);
+                let candidate_here = step(&here, d1, t1);
+                if map.contains_key(&candidate_here) {
+                    let mut ab_walk = walk.clone();
+
+                    for _ in 0..t1 { ab_walk.push(d1); }
+                    for _ in 0..t2 { ab_walk.push(d2); }
+
+                    new_out.push((ab_walk, end));
+                }
+
+                let candidate_there = step(&here, d2, t2);
+                if map.contains_key(&candidate_there) {
+                    let mut ba_walk = walk.clone();
+
+                    for _ in 0..t2 { ba_walk.push(d2); }
+                    for _ in 0..t1 { ba_walk.push(d1); }
+
+                    new_out.push((ba_walk, end));
+                }
+
+            }
+        } else {
+            panic!("encountered a bad set of choices");
+        }
+
+        out = new_out;
+    }
+
+    let mut final_out = vec![];
+    for (walk, _) in out {
+        final_out.push(walk);
+    }
+    return final_out;
+}
+
+fn shortest_sequences<T>(
+    options: Vec<Vec<(Dir, i32)>>, 
+    map: &HashMap<Coord, T>, 
+    start: Coord
+) -> Vec<Vec<Dir>> {
+    let mut short_length = None;
+    let mut shorts = vec![];
+
+    for seq in sequences(options.to_vec(), map, start) {
+        let my_len = seq.len();
+        if let Some(len) = short_length {
+            if my_len == len {
+                shorts.push(seq);
+            } else if my_len < len {
+                shorts = vec![seq];
+                short_length = Some(my_len);
+            }
+        } else {
+            short_length = Some(my_len);
+            shorts.push(seq);
+        }
+    }
+
+    return shorts;
+}
+
+fn build_options<T: std::hash::Hash + std::cmp::Eq>(
+    routes: &HashMap<(Coord, Coord), Vec<(Dir, i32)>>, 
+    map: &HashMap<T, Coord>,
+    sequence: &Vec<T>,
+    start: T,
+) -> Vec<Vec<(Dir, i32)>> {
+    let mut here = map[&start];
+    let mut options: Vec<Vec<(Dir, i32)>> = Vec::new();
+    for button in sequence {
+        let there = map[&button];
+        options.push(routes[&(here, there)].clone());
+        options.push(vec![(Stay, 1)]);
+        here = there;
+    }
+
+    return options;
+}
+
+
+fn print_code(code: &Vec<Dir>) {
+    for x in code {
+        print!("{}", match x { 
+            North => '^', South => 'v', East => '>', West => '<', Stay => 'A'
+        });
+    }
+    print!("\n");
+}
+
+fn print_code_door(code: &Vec<char>) {
+    for x in code {
+        print!("{}", x);
+    }
+    print!("\n");
+}
+
+
+fn execute_code<T: Clone + Copy>(
+    code: &Vec<Dir>, 
+    map: &HashMap<Coord, T>, 
+    start: Coord
+) -> Vec<T> {
+
+    let mut out = vec![];
+    let mut here = start;
+    for d in code {
+        if *d == Stay {
+            out.push(map[&here]);
+        } else {
+            here = step(&here, *d, 1);
+        }
+
+    }
+    return out;
+
+}
+
+
+
+