diff --git a/day17/src/main.rs b/day17/src/main.rs
index 0d82b41..7fd32e8 100644
--- a/day17/src/main.rs
+++ b/day17/src/main.rs
@@ -19,7 +19,7 @@ struct Shape {
 #[derive(Debug)]
 struct Pos {y: usize, x: usize}
 
-static SHAPE_NAMES: [char; 5] = ['-', '+', 'L', '|', '.'];
+//static SHAPE_NAMES: [char; 5] = ['-', '+', 'L', '|', '.'];
 static SHAPES: [Shape; 5] = [
     Shape { // -
         bot: [0, 0, 0, 0], top: [0, 0, 0, 0],
@@ -113,9 +113,11 @@ fn iterate(
 
 fn main() -> io::Result<()> {
     let input_fname = env::args().nth(1).expect("need input file");
+    let limit = env::args().nth(2).expect("need limit").parse::<usize>().unwrap();
     let mut winds: Vec<u8> = Vec::new();
     let _ = BufReader::new(File::open(input_fname)?).read_until(b'\n', &mut winds);
     if winds.last() == Some(&b'\n') { winds.pop(); }
+    println!("winds = {}, shapes = {}", winds.len(), SHAPES.len());
 
     let mut shape_id = 0;
     let mut shape = &SHAPES[shape_id];
@@ -127,13 +129,12 @@ fn main() -> io::Result<()> {
         [0, 0, 0, 0, 0, 0, 0],
         [0, 0, 0, 0, 0, 0, 0],
     ];
-    prettyprint(&map, &shape_pos, SHAPE_NAMES[shape_id]);
 
-    let mut nrocks = 0;
+    let mut answers: Vec<(usize, usize)> = Vec::new();
+
     let mut i = 0;
-    while nrocks < 2022 { //debug
+    'mainloop: while answers.len() < limit {
         let c = winds[i % winds.len()];
-        i += 1;
         if iterate(&mut map, shape, &mut shape_pos, c) {
             let last_shape_top = shape_pos.y + shape.height - 1;
             if last_shape_top > current_top {
@@ -141,28 +142,69 @@ fn main() -> io::Result<()> {
             }
             shape_id = (shape_id + 1) % SHAPES.len(); // next shape
             shape = &SHAPES[shape_id];
-            //println!("{} -> {}", map.len(), last_shape_top + 4 + shape.height);
             for _ in map.len()..(current_top + 4 + shape.height) {
                 map.push([0, 0, 0, 0, 0, 0, 0]);
             }
-            nrocks += 1;
             shape_pos = Pos{x:2, y: current_top + 4};
-            //println!("= {} ({})", current_top, nrocks);
-            prettyprint(&map, &shape_pos, SHAPE_NAMES[shape_id]);
+            answers.push((i, current_top));
+            let last_rock = answers.len() - 1;
+            print!(
+                "rock {} - (i {}, top {})",
+                last_rock, i, current_top
+            );
+
+            if last_rock >= 2*SHAPES.len() {
+                let mut j = last_rock - SHAPES.len();
+                'lookback: while j > (last_rock / 2) {
+                    let (hist_i, hist_top) = answers[j];
+                    let next_j = 2*j - last_rock;
+                    let (hist2_i, hist2_top) = answers[next_j];
+                    if (i - hist_i) % winds.len() == 0
+                        && (i - hist_i) == (hist_i - hist2_i)
+                        && (current_top - hist_top) == (hist_top - hist2_top) {
+                        print!(
+                            " {}-{}-{}-({}-{}-{})",
+                            j, hist_i, hist_top,
+                            next_j, hist2_i, hist2_top,
+                        );
+                        print!(
+                            " rock cycle {}, off {} | \
+                             top cycle {} off {} ",
+                            last_rock - j, next_j,
+                            current_top - hist_top, hist2_top,
+                        );
+                        if (limit - 1 - next_j) % (last_rock - j) == 0 {
+                            let n_cycles = (limit - 1 - next_j) / (last_rock - j);
+                            println!(
+                                "\nheight = {}",
+                                hist2_top + n_cycles*(current_top - hist_top) + 1
+                            );
+                            break 'mainloop;
+                        } else {
+                            break 'lookback;
+                        }
+                    }
+                    j -= SHAPES.len();
+                }
+
+            }
+
+            println!();
+            //prettyprint(&map, &shape_pos, SHAPE_NAMES[shape_id]);
         }
+        i += 1;
     }
-    println!("height = {}", current_top + 1);
     Ok(())
 }
 
 fn prettyprint(map: &Vec<[u8; 7]>, pos: &Pos, shape_name: char) {
-//     let mut i = map.len();
-//     for row in map.into_iter().rev() {
-//         i -= 1;
-//         print!("|");
-//         for j in 0..7 {
-//             print!("{}", if row[j] == 0 { "." } else { "#" });
-//         }
-//         println!("| {} {}", i, if i == pos.y {shape_name} else {' '});
-//     }
+    let mut i = map.len();
+    for row in map.into_iter().rev() {
+        i -= 1;
+        print!("|");
+        for j in 0..7 {
+            print!("{}", if row[j] == 0 { "." } else { "#" });
+        }
+        println!("| {} {}", i, if i == pos.y {shape_name} else {' '});
+    }
 }
diff --git a/day17/src/main1.rs b/day17/src/main1.rs
new file mode 100644
index 0000000..0d82b41
--- /dev/null
+++ b/day17/src/main1.rs
@@ -0,0 +1,168 @@
+use std::io;
+use std::env;
+use std::fs::File;
+use std::io::BufReader;
+use std::io::BufRead;
+use std::fmt::Debug;
+
+#[derive(Debug)]
+struct Shape {
+    bot: [i8; 4], // distance from datum. -1 for unused.
+    top: [i8; 4],
+    left: [i8; 4],
+    right: [i8; 4],
+    width: usize,
+    height: usize,
+}
+
+// a Shape's datum is its bottom left corner
+#[derive(Debug)]
+struct Pos {y: usize, x: usize}
+
+static SHAPE_NAMES: [char; 5] = ['-', '+', 'L', '|', '.'];
+static SHAPES: [Shape; 5] = [
+    Shape { // -
+        bot: [0, 0, 0, 0], top: [0, 0, 0, 0],
+        left: [0, -1, -1, -1], right: [3, -1, -1, -1],
+        width: 4, height: 1,
+    },
+    Shape { // +
+        bot: [1, 0, 1, -1], top: [1, 2, 1, -1],
+        left: [1, 0, 1, -1], right: [1, 2, 1, -1],
+        width: 3, height: 3,
+    },
+    Shape { // backward L
+        bot: [0, 0, 0, -1], top: [0, 0, 2, -1],
+        left: [0, 2, 2, -1], right: [2, 2, 2, -1],
+        width: 3, height: 3,
+    },
+    Shape { // |
+        bot: [0, -1, -1, -1], top: [0, -1, -1, -1],
+        left: [0, 0, 0, 0], right: [0, 0, 0, 0],
+        width: 1, height: 4,
+    },
+    Shape { // square
+        bot: [0, 0, -1, -1], top: [1, 1, -1, -1],
+        left: [0, 0, -1, -1], right: [1, 1, -1, -1],
+        width: 2, height: 2,
+    },
+];
+
+fn iterate(
+        map: &mut Vec<[u8; 7]>, shape: &Shape, pos: &mut Pos, wind: u8
+) -> bool {
+    //println!("  __ {}, start {:?}", wind as char, pos);
+    // Wind move
+    match wind {
+        b'>' => 'rightmove: {
+            if pos.x + shape.width == 7 { break 'rightmove; }
+            let mut i = 0;
+            while i < 4 && shape.right[i] >= 0 {
+                let right_point = pos.x + shape.right[i] as usize;
+                if right_point + 1 == 7 { break 'rightmove; }
+                if map[pos.y + i][right_point + 1] != 0 { break 'rightmove; }
+                i += 1;
+            }
+            pos.x += 1;
+            //println!("  >> {:?}", pos);
+        },
+        b'<' => 'leftmove: {
+            if pos.x == 0 { break 'leftmove; }
+            let mut i = 0;
+            while i < 4 && shape.left[i] >= 0 {
+                let left_point = pos.x + shape.left[i] as usize;
+                if left_point == 0 { break 'leftmove; }
+                if map[pos.y + i][left_point - 1] != 0 { break 'leftmove; }
+                i += 1;
+            }
+            pos.x -= 1;
+            //println!("  << {:?}", pos);
+        },
+        _ => panic!(),
+    }
+
+    // Gravity move
+    'downmove: {
+        let mut i = 0;
+        while i < 4 && shape.bot[i] >= 0 {
+            let bot_point = pos.y + shape.bot[i] as usize;
+            if bot_point == 0 { break 'downmove; }
+            if map[bot_point - 1][pos.x + i] != 0 { break 'downmove; }
+            i += 1;
+        }
+        pos.y -= 1;
+        //println!("  vv {:?}", pos);
+        return false;
+    }
+
+    // Settling
+    let mut i = 0;
+    while i < 4 && shape.left[i] >= 0 && shape.right[i] >= 0 {
+        map[pos.y + i][pos.x + shape.left[i] as usize] = 1;
+        map[pos.y + i][pos.x + shape.right[i] as usize] = 1;
+        i += 1;
+    }
+    i = 0;
+    while i < 4 && shape.top[i] >= 0 && shape.bot[i] >= 0 {
+        map[pos.y + shape.top[i] as usize][pos.x + i] = 1;
+        map[pos.y + shape.bot[i] as usize][pos.x + i] = 1;
+        i += 1;
+    }
+    return true;
+}
+
+fn main() -> io::Result<()> {
+    let input_fname = env::args().nth(1).expect("need input file");
+    let mut winds: Vec<u8> = Vec::new();
+    let _ = BufReader::new(File::open(input_fname)?).read_until(b'\n', &mut winds);
+    if winds.last() == Some(&b'\n') { winds.pop(); }
+
+    let mut shape_id = 0;
+    let mut shape = &SHAPES[shape_id];
+    let mut current_top = 0;
+    let mut shape_pos = Pos{x: 2, y: 3};
+    let mut map: Vec<[u8; 7]> = vec![
+        [0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 0, 0, 0, 0],
+        [0, 0, 0, 0, 0, 0, 0],
+    ];
+    prettyprint(&map, &shape_pos, SHAPE_NAMES[shape_id]);
+
+    let mut nrocks = 0;
+    let mut i = 0;
+    while nrocks < 2022 { //debug
+        let c = winds[i % winds.len()];
+        i += 1;
+        if iterate(&mut map, shape, &mut shape_pos, c) {
+            let last_shape_top = shape_pos.y + shape.height - 1;
+            if last_shape_top > current_top {
+                current_top = last_shape_top;
+            }
+            shape_id = (shape_id + 1) % SHAPES.len(); // next shape
+            shape = &SHAPES[shape_id];
+            //println!("{} -> {}", map.len(), last_shape_top + 4 + shape.height);
+            for _ in map.len()..(current_top + 4 + shape.height) {
+                map.push([0, 0, 0, 0, 0, 0, 0]);
+            }
+            nrocks += 1;
+            shape_pos = Pos{x:2, y: current_top + 4};
+            //println!("= {} ({})", current_top, nrocks);
+            prettyprint(&map, &shape_pos, SHAPE_NAMES[shape_id]);
+        }
+    }
+    println!("height = {}", current_top + 1);
+    Ok(())
+}
+
+fn prettyprint(map: &Vec<[u8; 7]>, pos: &Pos, shape_name: char) {
+//     let mut i = map.len();
+//     for row in map.into_iter().rev() {
+//         i -= 1;
+//         print!("|");
+//         for j in 0..7 {
+//             print!("{}", if row[j] == 0 { "." } else { "#" });
+//         }
+//         println!("| {} {}", i, if i == pos.y {shape_name} else {' '});
+//     }
+}