diff --git a/2021/input/2021/day19.txt b/2021/input/2021/day19.txt
new file mode 100644
index 0000000..e55cd09
--- /dev/null
+++ b/2021/input/2021/day19.txt
@@ -0,0 +1,1054 @@
+--- scanner 0 ---
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+--- scanner 1 ---
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+--- scanner 13 ---
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+--- scanner 28 ---
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+--- scanner 29 ---
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+--- scanner 30 ---
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+--- scanner 31 ---
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+--- scanner 32 ---
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+--- scanner 33 ---
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+--- scanner 34 ---
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+--- scanner 35 ---
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+746,-448,-686
+
+--- scanner 36 ---
+-310,675,-866
+-311,610,-746
+-298,-533,-507
+421,-788,-656
+860,368,816
+829,374,761
+783,370,808
+-509,-717,796
+-489,-794,806
+427,-906,-540
+726,-381,858
+660,790,-629
+781,705,-604
+-14,55,82
+-258,542,-859
+606,-475,860
+-791,632,616
+-741,539,626
+-413,-427,-471
+-723,569,754
+-515,-797,608
+377,-747,-573
+654,-425,701
+-269,-420,-505
+681,812,-544
+95,-98,30
+
+--- scanner 37 ---
+473,-578,819
+-940,881,-381
+-912,776,-403
+-400,586,662
+482,-578,-649
+-830,-487,741
+-463,486,559
+-585,-355,-626
+-700,-373,-531
+547,-606,-529
+-793,-591,743
+704,806,-783
+676,-520,-608
+-674,-507,720
+761,500,535
+-111,-17,198
+800,619,431
+714,501,435
+469,-694,777
+465,-550,734
+585,837,-766
+-458,501,654
+-669,-441,-653
+-38,40,27
+-860,800,-384
+622,887,-649
diff --git a/2021/input/2021/day23.txt b/2021/input/2021/day23.txt
new file mode 100644
index 0000000..0140289
--- /dev/null
+++ b/2021/input/2021/day23.txt
@@ -0,0 +1,5 @@
+#############
+#...........#
+###D#A#C#D###
+  #C#A#B#B#
+  #########
diff --git a/2021/src/day19.rs b/2021/src/day19.rs
new file mode 100644
index 0000000..9f7e4ea
--- /dev/null
+++ b/2021/src/day19.rs
@@ -0,0 +1,469 @@
+use advent::prelude::*;
+use aoc_runner_derive::aoc;
+use std::ops::{Add, Sub};
+
+#[derive(Clone, Copy, Default, Eq, Hash, PartialEq, PartialOrd, Ord)]
+struct Vec3([i64; 3]);
+
+impl Add for Vec3 {
+    type Output = Self;
+    fn add(self, other: Self) -> Self::Output {
+        Vec3([
+            self.0[0] + other.0[0],
+            self.0[1] + other.0[1],
+            self.0[2] + other.0[2],
+        ])
+    }
+}
+
+impl Sub for Vec3 {
+    type Output = Self;
+    fn sub(self, other: Self) -> Self::Output {
+        Vec3([
+            self.0[0] - other.0[0],
+            self.0[1] - other.0[1],
+            self.0[2] - other.0[2],
+        ])
+    }
+}
+
+impl Debug for Vec3 {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
+        write!(f, "<{:4},{:4},{:4}>", self.0[0], self.0[1], self.0[2])
+    }
+}
+
+impl FromStr for Vec3 {
+    type Err = Infallible;
+
+    fn from_str(input: &str) -> std::result::Result<Vec3, Infallible> {
+        let v: Vec<_> = input.split(',').map(|s| s.parse().unwrap()).collect();
+        Ok(Vec3(v.try_into().unwrap()))
+    }
+}
+
+#[derive(Debug)]
+struct Scanner {
+    id: usize,
+    offset: Option<Vec3>,
+    points: Vec<Vec3>,
+}
+
+impl Scanner {
+    fn translate(&mut self, distance: Vec3, orientation: [usize; 3], signs: [i64; 3]) {
+        for p in &mut self.points {
+            *p = Vec3([
+                signs[0] * p.0[orientation[0]] + distance.0[0],
+                signs[1] * p.0[orientation[1]] + distance.0[1],
+                signs[2] * p.0[orientation[2]] + distance.0[2],
+            ]);
+        }
+    }
+}
+
+impl FromStr for Scanner {
+    type Err = Infallible;
+
+    fn from_str(input: &str) -> std::result::Result<Scanner, Infallible> {
+        let mut it = input.lines();
+        let id = it
+            .next()
+            .unwrap()
+            .split(' ')
+            .nth(2)
+            .unwrap()
+            .parse()
+            .unwrap();
+        Ok(Scanner {
+            id,
+            offset: None,
+            points: it.map(|l| l.parse().unwrap()).collect(),
+        })
+    }
+}
+
+#[derive(Debug, PartialEq)]
+struct Match {
+    abs_points: Vec<Vec3>,
+    distance: Vec3,
+    orientation: [usize; 3],
+    signs: [i64; 3],
+}
+
+// Returns overlap, and  in s1 space
+fn find_overlap(s1: &Scanner, s2: &Scanner) -> Option<Match> {
+    let mut counts: HashMap<(Vec3, [usize; 3], [i64; 3]), Vec<Vec3>> = HashMap::new();
+    let orientations = [
+        [0, 1, 2],
+        [0, 2, 1],
+        [1, 0, 2],
+        [1, 2, 0],
+        [2, 0, 1],
+        [2, 1, 0],
+    ];
+    let signs = [
+        [-1, -1, -1],
+        [1, -1, -1],
+        [-1, 1, -1],
+        [1, 1, -1],
+        [-1, -1, 1],
+        [1, -1, 1],
+        [-1, 1, 1],
+    ];
+    for v1 in &s1.points {
+        for v2 in &s2.points {
+            for or in orientations {
+                for sign in signs {
+                    let [x, y, z] = sign;
+                    let v = Vec3([x * v2.0[or[0]], y * v2.0[or[1]], z * v2.0[or[2]]]);
+                    let diff = *v1 - v;
+                    counts.entry((diff, or, sign)).or_default().push(*v1);
+                }
+            }
+        }
+    }
+    if let Some(((distance, orientation, signs), list)) =
+        counts.into_iter().find(|(_k, v)| v.len() >= 12)
+    {
+        // s1's points should already be in absolute coords.  s2 will be translated in
+        // part1().
+        return Some(Match {
+            abs_points: list,
+            distance,
+            orientation,
+            signs,
+        });
+    }
+    None
+}
+
+fn parse(input: &str) -> Result<Vec<Scanner>> {
+    input.split("\n\n").map(|s| Ok(s.parse()?)).collect()
+}
+#[aoc(day19, part1)]
+fn part1(input: &str) -> Result<usize> {
+    let mut scanner = parse(input)?;
+    // Assign the first scanner to the origin (0,0,0).
+    // Put that in a list of recently registered scanners.
+    // In a loop
+    // - For each recently registered scanner, attempt to find overlap with each unregistered
+    // scanner.
+    // - Matches should be translated according to the offsets found during the match. This should
+    // put them in absolute space.
+    // - Each match should be added to the recently registered list for the next iteration.
+    // - Do this until all scanners are registered.
+    scanner[0].offset = Some(Vec3::default());
+    let (mut registered, mut unregistered): (VecDeque<_>, VecDeque<_>) =
+        scanner.into_iter().partition(|s| s.offset.is_some());
+
+    let mut becons = HashSet::new();
+    let mut done = Vec::new();
+    while let Some(reg) = registered.pop_front() {
+        let mut unregs = VecDeque::new();
+        for mut unreg in unregistered {
+            if let Some(mat) = find_overlap(&reg, &unreg) {
+                unreg.offset = Some(mat.distance);
+                unreg.translate(mat.distance, mat.orientation, mat.signs);
+                println!(
+                    "scanner {} @ {:?} found {} hits",
+                    &unreg.id,
+                    &unreg.offset.unwrap(),
+                    mat.abs_points.len()
+                );
+                registered.push_back(unreg);
+                for pt in mat.abs_points {
+                    becons.insert(pt);
+                }
+            } else {
+                unregs.push_back(unreg);
+            }
+        }
+        done.push(reg);
+        unregistered = unregs;
+    }
+
+    println!("before pass 2: {}", becons.len());
+    for i in 0..registered.len() {
+        for j in i..registered.len() {
+            let s1 = &registered[i];
+            let s2 = &registered[j];
+            if let Some(mat) = find_overlap(s1, s2) {
+                for pt in mat.abs_points {
+                    becons.insert(pt);
+                }
+            }
+        }
+    }
+    println!("after pass 2: {}", becons.len());
+
+    //assert_eq!(done.len(), 12);
+    let mut becons: Vec<_> = becons.iter().collect();
+    becons.sort();
+    dbg!(&becons);
+    Ok(becons.len())
+}
+
+/*
+#[aoc(day19, part2)]
+fn part2(input: &str) -> Result<usize> {
+todo!("part2");
+Ok(0)
+}
+*/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_overlap() -> Result<()> {
+        use pretty_assertions::assert_eq;
+
+        let input = r#"
+--- scanner 0 ---
+404,-588,-901
+528,-643,409
+-838,591,734
+390,-675,-793
+-537,-823,-458
+-485,-357,347
+-345,-311,381
+-661,-816,-575
+-876,649,763
+-618,-824,-621
+553,345,-567
+474,580,667
+-447,-329,318
+-584,868,-557
+544,-627,-890
+564,392,-477
+455,729,728
+-892,524,684
+-689,845,-530
+423,-701,434
+7,-33,-71
+630,319,-379
+443,580,662
+-789,900,-551
+459,-707,401
+
+--- scanner 1 ---
+686,422,578
+605,423,415
+515,917,-361
+-336,658,858
+95,138,22
+-476,619,847
+-340,-569,-846
+567,-361,727
+-460,603,-452
+669,-402,600
+729,430,532
+-500,-761,534
+-322,571,750
+-466,-666,-811
+-429,-592,574
+-355,545,-477
+703,-491,-529
+-328,-685,520
+413,935,-424
+-391,539,-444
+586,-435,557
+-364,-763,-893
+807,-499,-711
+755,-354,-619
+553,889,-390
+"#
+        .trim();
+        let mut abs_points: Vec<Vec3> = r#"
+-618,-824,-621
+-537,-823,-458
+-447,-329,318
+404,-588,-901
+544,-627,-890
+528,-643,409
+-661,-816,-575
+390,-675,-793
+423,-701,434
+-345,-311,381
+459,-707,401
+-485,-357,347
+"#
+        .trim()
+        .lines()
+        .map(|l| l.parse().unwrap())
+        .collect();
+        abs_points.sort();
+        let orientation = [0, 1, 2];
+        let signs = [-1, 1, -1];
+        let distance = Vec3([68, -1246, -43]);
+        let want = Match {
+            distance,
+            abs_points,
+            orientation,
+            signs,
+        };
+
+        let scanners = parse(input)?;
+        let mut got = find_overlap(&scanners[0], &scanners[1]).unwrap();
+        got.abs_points.sort();
+        assert_eq!(want, got);
+        Ok(())
+    }
+
+    #[test]
+    fn test_part1() -> Result<()> {
+        let input = r#"
+--- scanner 0 ---
+404,-588,-901
+528,-643,409
+-838,591,734
+390,-675,-793
+-537,-823,-458
+-485,-357,347
+-345,-311,381
+-661,-816,-575
+-876,649,763
+-618,-824,-621
+553,345,-567
+474,580,667
+-447,-329,318
+-584,868,-557
+544,-627,-890
+564,392,-477
+455,729,728
+-892,524,684
+-689,845,-530
+423,-701,434
+7,-33,-71
+630,319,-379
+443,580,662
+-789,900,-551
+459,-707,401
+
+--- scanner 1 ---
+686,422,578
+605,423,415
+515,917,-361
+-336,658,858
+95,138,22
+-476,619,847
+-340,-569,-846
+567,-361,727
+-460,603,-452
+669,-402,600
+729,430,532
+-500,-761,534
+-322,571,750
+-466,-666,-811
+-429,-592,574
+-355,545,-477
+703,-491,-529
+-328,-685,520
+413,935,-424
+-391,539,-444
+586,-435,557
+-364,-763,-893
+807,-499,-711
+755,-354,-619
+553,889,-390
+
+--- scanner 2 ---
+649,640,665
+682,-795,504
+-784,533,-524
+-644,584,-595
+-588,-843,648
+-30,6,44
+-674,560,763
+500,723,-460
+609,671,-379
+-555,-800,653
+-675,-892,-343
+697,-426,-610
+578,704,681
+493,664,-388
+-671,-858,530
+-667,343,800
+571,-461,-707
+-138,-166,112
+-889,563,-600
+646,-828,498
+640,759,510
+-630,509,768
+-681,-892,-333
+673,-379,-804
+-742,-814,-386
+577,-820,562
+
+--- scanner 3 ---
+-589,542,597
+605,-692,669
+-500,565,-823
+-660,373,557
+-458,-679,-417
+-488,449,543
+-626,468,-788
+338,-750,-386
+528,-832,-391
+562,-778,733
+-938,-730,414
+543,643,-506
+-524,371,-870
+407,773,750
+-104,29,83
+378,-903,-323
+-778,-728,485
+426,699,580
+-438,-605,-362
+-469,-447,-387
+509,732,623
+647,635,-688
+-868,-804,481
+614,-800,639
+595,780,-596
+
+--- scanner 4 ---
+727,592,562
+-293,-554,779
+441,611,-461
+-714,465,-776
+-743,427,-804
+-660,-479,-426
+832,-632,460
+927,-485,-438
+408,393,-506
+466,436,-512
+110,16,151
+-258,-428,682
+-393,719,612
+-211,-452,876
+808,-476,-593
+-575,615,604
+-485,667,467
+-680,325,-822
+-627,-443,-432
+872,-547,-609
+833,512,582
+807,604,487
+839,-516,451
+891,-625,532
+-652,-548,-490
+30,-46,-14
+"#
+        .trim();
+        assert_eq!(part1(input)?, 79);
+        Ok(())
+    }
+
+    /*
+    #[test]
+    fn test_part2()->Result<()> {
+    let input = r#"
+    "#
+    .trim();
+    assert_eq!(part2(input)?, usize::MAX);
+    Ok(())
+    }
+    */
+}
diff --git a/2021/src/day23.rs b/2021/src/day23.rs
new file mode 100644
index 0000000..4afae42
--- /dev/null
+++ b/2021/src/day23.rs
@@ -0,0 +1,41 @@
+use advent::prelude::*;
+use aoc_runner_derive::aoc;
+
+#[aoc(day23, part1)]
+fn part1(input: &str) -> Result<usize> {
+    todo!("part1");
+    Ok(0)
+}
+
+/*
+#[aoc(day23, part2)]
+fn part2(input: &str) -> Result<usize> {
+    todo!("part2");
+    Ok(0)
+}
+*/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part1() -> Result<()> {
+        let input = r#"
+"#
+        .trim();
+        assert_eq!(part1(input)?, usize::MAX);
+        Ok(())
+    }
+
+    /*
+    #[test]
+    fn test_part2()->Result<()> {
+        let input = r#"
+    "#
+        .trim();
+        assert_eq!(part2(input)?, usize::MAX);
+    Ok(())
+    }
+    */
+}
diff --git a/2021/src/lib.rs b/2021/src/lib.rs
index cde02ad..33a982f 100644
--- a/2021/src/lib.rs
+++ b/2021/src/lib.rs
@@ -8,10 +8,12 @@ pub mod day15;
 pub mod day16;
 pub mod day17;
 //pub mod day18;
+pub mod day19;
 pub mod day2;
 pub mod day20;
 pub mod day21;
 pub mod day22;
+//pub mod day23;
 pub mod day3;
 pub mod day4;
 pub mod day5;
diff --git a/rustfmt.toml b/rustfmt.toml
index c3c8c37..bcd436a 100644
--- a/rustfmt.toml
+++ b/rustfmt.toml
@@ -1 +1,2 @@
 imports_granularity = "Crate"
+format_code_in_doc_comments = true
diff --git a/src/lib.rs b/src/lib.rs
index be37bf1..7c5ba58 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,6 @@
 pub mod prelude {
     pub use std::{
-        collections::{HashMap, HashSet},
+        collections::{HashMap, HashSet, VecDeque},
         convert::Infallible,
         fmt::{Debug, Display, Error, Formatter},
         io::Read,