Days 8 and 9

12 files changed, 2626 insertions, 0 deletions

diff --git a/08/Cargo.toml b/08/Cargo.toml
new file mode 100644
index 0000000..644d264
--- /dev/null
+++ b/08/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "day-08"
+version = "0.1.0"
+authors = ["Gard Spreemann <gspr@nonempty.org>"]
+edition = "2021"
+
+[[bin]]
+name = "part-1"
+path = "src/part-1.rs"
+
+[[bin]]
+name = "part-2"
+path = "src/part-2.rs"
+
+[dependencies]
diff --git a/08/input.txt b/08/input.txt
new file mode 100644
index 0000000..d46e623
--- /dev/null
+++ b/08/input.txt
@@ -0,0 +1,99 @@
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diff --git a/08/src/part-1.rs b/08/src/part-1.rs
new file mode 100644
index 0000000..1bbd75a
--- /dev/null
+++ b/08/src/part-1.rs
@@ -0,0 +1,91 @@
+mod tensor;
+
+use std::io::{BufRead};
+
+use tensor::{Index, Shape, Tensor};
+
+fn main() {
+    let stdin = std::io::stdin();
+    let mut handle = stdin.lock();
+
+    let mut tmp: Vec<(i8, bool)> = Vec::new();
+    let mut m: usize = 0;
+    let mut n: usize = 0;
+    let mut n_check: usize = 0;
+    
+    loop {
+        let buf = handle.fill_buf().expect("IO error");
+        let bytes_read = buf.len();
+        if bytes_read == 0 { break; }
+
+        for & b in buf.into_iter() {
+            if b >= b'0' && b <= b'9' {
+                tmp.push(((b - b'0').try_into().unwrap(), false));
+                if m == 0 {
+                    n += 1;
+                }
+                n_check += 1;
+            }
+            if b == b'\n' {
+                m += 1;
+                assert_eq!(n_check, n);
+                n_check = 0;
+            }
+        }
+
+        handle.consume(bytes_read);
+    }
+
+    let mut x: Tensor<(i8, bool), 2> = Tensor::new_from([m, n], tmp);
+    let shape = x.shape().clone();
+    let mut tallest: i8;
+
+    // Look north-south.
+    for j in 0..shape[1] {
+        // Look from north.
+        tallest = -1;
+        for i in 0..shape[0] {
+            let tree = &mut x[[i, j]];
+            if tree.0 > tallest {
+                tree.1 = true;
+                tallest = tree.0;
+            }
+        }
+
+        // Look from south.
+        tallest = -1;
+        for i in (0..shape[0]).rev() {
+            let tree = &mut x[[i, j]];
+            if tree.0 > tallest {
+                tree.1 = true;
+                tallest = tree.0;
+            }
+        }
+    }
+
+    // Look east-west.
+    for i in 0..shape[0] {
+        // Look from west.
+        tallest = -1;
+        for j in 0..shape[1] {
+            let tree = &mut x[[i, j]];
+            if tree.0 > tallest {
+                tree.1 = true;
+                tallest = tree.0;
+            }
+        }
+
+        // Look from east.
+        tallest = -1;
+        for j in (0..shape[1]).rev() {
+            let tree = &mut x[[i, j]];
+            if tree.0 > tallest {
+                tree.1 = true;
+                tallest = tree.0;
+            }
+        }
+    }
+
+    let num_visible = x.data().into_iter().filter(|(_, vis)| *vis).count();
+    println!("{}", num_visible);
+}
diff --git a/08/src/part-2.rs b/08/src/part-2.rs
new file mode 100644
index 0000000..94bf4d5
--- /dev/null
+++ b/08/src/part-2.rs
@@ -0,0 +1,90 @@
+mod tensor;
+
+use std::cmp::{max};
+use std::io::{BufRead};
+
+use tensor::{Index, Shape, Tensor};
+
+fn main() {
+    let stdin = std::io::stdin();
+    let mut handle = stdin.lock();
+
+    let mut tmp: Vec<usize> = Vec::new();
+    let mut m: usize = 0;
+    let mut n: usize = 0;
+    let mut n_check: usize = 0;
+    
+    loop {
+        let buf = handle.fill_buf().expect("IO error");
+        let bytes_read = buf.len();
+        if bytes_read == 0 { break; }
+
+        for & b in buf.into_iter() {
+            if b >= b'0' && b <= b'9' {
+                tmp.push((b - b'0').try_into().unwrap());
+                if m == 0 {
+                    n += 1;
+                }
+                n_check += 1;
+            }
+            if b == b'\n' {
+                m += 1;
+                assert_eq!(n_check, n);
+                n_check = 0;
+            }
+        }
+
+        handle.consume(bytes_read);
+    }
+
+    let mut x: Tensor<usize, 2> = Tensor::new_from([m, n], tmp);
+    let shape = x.shape().clone();
+
+    let mut highest_score: usize = 0;
+
+    for i in 0..m {
+        for j in 0..n {
+            let h = x[[i, j]];
+            
+            // Look north
+            let mut north_dist = 0;
+            for a in (0..i).rev() {
+                north_dist += 1;
+                if x[[a, j]] >= h {
+                    break;
+                }
+            }
+
+            // Look south.
+            let mut south_dist = 0;
+            for a in i+1..m {
+                south_dist += 1;
+                if x[[a, j]] >= h {
+                    break;
+                }
+            }
+
+            // Look east.
+            let mut east_dist = 0;
+            for a in j+1..n {
+                east_dist += 1;
+                if x[[i, a]] >= h {
+                    break;
+                }
+            }
+
+            // Look west.
+            let mut west_dist = 0;
+            for a in (0..j).rev() {
+                west_dist += 1;
+                if x[[i, a]] >= h {
+                    break;
+                }
+            }
+
+            highest_score = max(highest_score, north_dist*south_dist*east_dist*west_dist);
+        }
+    }
+
+    println!("{}", highest_score);
+}
diff --git a/08/src/tensor.rs b/08/src/tensor.rs
new file mode 100644
index 0000000..2635886
--- /dev/null
+++ b/08/src/tensor.rs
@@ -0,0 +1,171 @@
+#![allow(dead_code)]
+
+pub type Shape<const D: usize> = [usize; D];
+pub type Index<const D: usize> = Shape<D>;
+
+pub struct Tensor<T, const D: usize> {
+    data: Vec<T>,
+    shape: Shape<D>,
+    strides: Shape<D>
+}
+
+pub type Tensor1<T> = Tensor<T, 1>;
+pub type Tensor2<T> = Tensor<T, 2>;
+pub type Tensor3<T> = Tensor<T, 3>;
+pub type Tensor4<T> = Tensor<T, 4>;
+pub type Index1 = Index<1>;
+pub type Index2 = Index<2>;
+pub type Index3 = Index<3>;
+pub type Index4 = Index<4>;
+
+
+impl<T: Copy, const D: usize> Tensor<T, D> {
+    pub fn new(shape: Shape<D>, x: T) -> Self {
+        if D == 0 { panic!("Empty shape not allowed."); }
+        
+        let mut len = shape[D-1];
+        let mut strides: Shape<D> = [0; D];
+        strides[D-1] = 1;
+        for d in (1..D).rev() { // d=D-1, …, 1.
+            strides[d-1] = shape[d]*strides[d];
+            len *= shape[d-1];
+        }
+        if len == 0 { panic!("Empty dimensions not allowed."); }
+        
+        Self {
+            data: vec![x; len],
+            shape: shape,
+            strides: strides,
+        }
+    }
+
+    pub fn new_from(shape: Shape<D>, x: Vec<T>) -> Self {
+        if D == 0 { panic!("Empty shape not allowed."); }
+        
+        let mut len = shape[D-1];
+        let mut strides: Shape<D> = [0; D];
+        strides[D-1] = 1;
+        for d in (1..D).rev() { // d=D-1, …, 1.
+            strides[d-1] = shape[d]*strides[d];
+            len *= shape[d-1];
+        }
+        if len == 0 { panic!("Empty dimensions not allowed."); }
+
+        if len != x.len() { panic!("Vector of length {} cannot fill tensor with {} entries.", x.len(), len); }
+
+        Self {
+            data: x,
+            shape: shape,
+            strides: strides,
+        }
+    }
+
+
+    #[inline(always)]
+    fn flatten_idx(self: & Self, idx: & Index<D>) -> usize {
+        // NOTE: This is a very hot code path. Should benchmark versus explicit loop.
+        idx.iter().zip(self.strides.iter()).fold(0, |sum, (i, s)| sum + i*s)
+    }
+
+    fn bound_check_panic(self: & Self, idx: & Index<D>) -> () {
+        for d in 0..D {
+            let i = *(unsafe { idx.get_unchecked(d) });
+            if i >= self.shape[d] {
+                panic!("{}-dimensional tensor index is out of bounds in dimension {} ({} >= {}).", D, d, i, self.shape[d])
+            }
+        }
+    }
+
+    pub fn in_bounds(self: & Self, idx: & Index<D>) -> bool {
+        for d in 0..D {
+            let i = *(unsafe { idx.get_unchecked(d) });
+            if i >= self.shape[d] {
+                return false;
+            }
+        }
+        true
+    }
+
+    pub fn shape(self: & Self) -> & Shape<D> { &self.shape }
+
+    pub fn el(self: & Self, idx: & Index<D>) -> Option<& T> {
+        if self.in_bounds(idx) { Some(unsafe { self.el_unchecked(idx) }) }
+        else                   { None }
+    }
+
+    pub unsafe fn el_unchecked(self: & Self, idx: & Index<D>) -> & T { self.data.get_unchecked(self.flatten_idx(idx)) }
+
+    pub unsafe fn el_unchecked_mut(self: &mut Self, idx: & Index<D>) -> &mut T {
+        let flat_idx = self.flatten_idx(idx);
+        self.data.get_unchecked_mut(flat_idx)
+    }
+
+    pub fn flat_len(self: & Self) -> usize { self.data.len() }
+    pub fn size(self: & Self) -> usize { self.flat_len()*std::mem::size_of::<T>() }
+
+    pub fn fill_with(self: &mut Self, x: & [T]) -> () {
+        // Already panics on size mismatch.
+        self.data.copy_from_slice(x)
+    }
+
+    pub fn fill(self: &mut Self, x: T) -> () {
+        self.data.fill(x);
+    }
+
+    pub fn data(self: & Self) -> & [T] { & self.data }
+}
+
+impl<T: Copy + std::fmt::Display> Tensor<T, 2> {
+    pub fn dirty_print(self: & Self) {
+        for i in 0..self.shape[0] {
+            for j in 0..self.shape[1] {
+                print!("{} ", self[[i, j]]);
+            }
+            println!("");
+        }
+    }
+}
+
+impl<T: Copy, const D: usize> std::ops::Index<Index<D>> for Tensor<T, D> {
+    type Output = T;
+
+    fn index(self: & Self, idx: Index<D>) -> & Self::Output {
+        self.bound_check_panic(&idx);
+        unsafe { self.el_unchecked(&idx) }
+    }
+}
+
+impl<T: Copy, const D: usize> std::ops::Index<& Index<D>> for Tensor<T, D> {
+    type Output = T;
+
+    fn index(self: & Self, idx: & Index<D>) -> & Self::Output {
+        self.bound_check_panic(idx);
+        unsafe { self.el_unchecked(idx) }
+    }
+}
+
+impl<T: Copy, const D: usize> std::ops::IndexMut<Index<D>> for Tensor<T, D> {
+    fn index_mut(self: &mut Self, idx: Index<D>) -> &mut Self::Output {
+        self.bound_check_panic(&idx);
+        unsafe { self.el_unchecked_mut(&idx) }
+    }
+}
+
+impl<T: Copy, const D: usize> std::ops::IndexMut<& Index<D>> for Tensor<T, D> {
+    fn index_mut(self: &mut Self, idx: & Index<D>) -> &mut Self::Output {
+        self.bound_check_panic(idx);
+        unsafe { self.el_unchecked_mut(idx) }
+    }
+}
+
+impl<T: Copy, const D: usize> IntoIterator for Tensor<T, D> {
+    type Item = T;
+    type IntoIter = std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter { self.data.into_iter() }
+}
+
+
+// FIXME: Should have a proper IntoIter implementing IntoIter for &'a Tensor<T, D>.
+
+// Note: Tensor is also sliceable (due to the Index implementations)
diff --git a/08/test.txt b/08/test.txt
new file mode 100644
index 0000000..16d6fbd
--- /dev/null
+++ b/08/test.txt
@@ -0,0 +1,5 @@
+30373
+25512
+65332
+33549
+35390
diff --git a/09/Cargo.toml b/09/Cargo.toml
new file mode 100644
index 0000000..100567b
--- /dev/null
+++ b/09/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "day-09"
+version = "0.1.0"
+authors = ["Gard Spreemann <gspr@nonempty.org>"]
+edition = "2021"
+
+[[bin]]
+name = "part-1"
+path = "src/part-1.rs"
+
+[[bin]]
+name = "part-2"
+path = "src/part-2.rs"
+
+[dependencies]
diff --git a/09/input.txt b/09/input.txt
new file mode 100644
index 0000000..68e6657
--- /dev/null
+++ b/09/input.txt
@@ -0,0 +1,2000 @@
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diff --git a/09/src/part-1.rs b/09/src/part-1.rs
new file mode 100644
index 0000000..f61c09d
--- /dev/null
+++ b/09/src/part-1.rs
@@ -0,0 +1,59 @@
+use std::collections::{HashSet};
+use std::io::{BufRead};
+
+
+fn main() {
+    let stdin = std::io::stdin();
+    let mut handle = stdin.lock();
+
+    let mut buf: Vec<u8> = Vec::new();
+    let mut seen: HashSet<[isize; 2]> = HashSet::new();
+    let mut head_pos: [isize; 2] = [0; 2];
+    let mut tail_pos: [isize; 2] = head_pos.clone();
+    seen.insert(tail_pos.clone());
+
+    loop {
+        buf.clear();
+        let num_bytes = handle.read_until(b'\n', &mut buf).expect("IO error");
+        if num_bytes == 0 { break; }
+
+        if buf[buf.len() - 1] == b'\n' { buf.pop(); }
+
+        let direction = buf[0];
+        let num_steps: usize = std::str::from_utf8(& buf[2..]).expect("Malformed input")
+            .parse().expect("Malformed input");
+
+        for dir in std::iter::repeat(direction).take(num_steps) {
+            match dir {
+                b'L' => head_pos[0] -= 1,
+                b'R' => head_pos[0] += 1,
+                b'U' => head_pos[1] += 1,
+                b'D' => head_pos[1] -= 1,
+                _    => panic!("Malformed input")
+            };
+            let delta: [isize; 2] = {
+                let mut ret: [isize; 2] = [0; 2];
+                for i in 0..2 { ret[i] = head_pos[i] - tail_pos[i]; }
+                ret
+            };
+            if delta[0].abs() == 2 {
+                tail_pos[0] += delta[0].signum();
+                if delta[1].abs() == 1 {
+                    tail_pos[1] += delta[1].signum();
+                }
+                seen.insert(tail_pos.clone());
+            }
+            else if delta[1].abs() == 2 {
+                tail_pos[1] += delta[1].signum();
+                if delta[0].abs() == 1 {
+                    tail_pos[0] += delta[0].signum();
+                }
+                seen.insert(tail_pos.clone());
+            }
+        }
+    }
+
+    println!("{}", seen.len());
+
+    
+}
diff --git a/09/src/part-2.rs b/09/src/part-2.rs
new file mode 100644
index 0000000..1773d2e
--- /dev/null
+++ b/09/src/part-2.rs
@@ -0,0 +1,65 @@
+// Ugh, weird motion in this grid world!
+
+use std::collections::{HashSet};
+use std::io::{BufRead};
+
+const NUM_SEGMENTS: usize = 10;
+
+type Pos = [isize; 2];
+
+fn main() {
+    let stdin = std::io::stdin();
+    let mut handle = stdin.lock();
+
+    let mut buf: Vec<u8> = Vec::new();
+    let mut seen: HashSet<[isize; 2]> = HashSet::new();
+    let mut positions: [Pos; NUM_SEGMENTS] = [[0; 2]; NUM_SEGMENTS];
+    seen.insert(positions[NUM_SEGMENTS-1].clone());
+
+    loop {
+        buf.clear();
+        let num_bytes = handle.read_until(b'\n', &mut buf).expect("IO error");
+        if num_bytes == 0 { break; }
+
+        if buf[buf.len() - 1] == b'\n' { buf.pop(); }
+
+        let direction = buf[0];
+        let num_steps: usize = std::str::from_utf8(& buf[2..]).expect("Malformed input")
+            .parse().expect("Malformed input");
+
+        for dir in std::iter::repeat(direction).take(num_steps) {
+            match dir {
+                b'L' => positions[0][0] -= 1,
+                b'R' => positions[0][0] += 1,
+                b'U' => positions[0][1] += 1,
+                b'D' => positions[0][1] -= 1,
+                _    => panic!("Malformed input")
+            };
+
+            for i in 1..NUM_SEGMENTS {
+                let delta: [isize; 2] = {
+                    let mut ret: [isize; 2] = [0; 2];
+                    for d in 0..2 { ret[d] = positions[i-1][d] - positions[i][d]; }
+                    ret
+                };
+                if delta[0].abs() == 2 {
+                    positions[i][0] += delta[0].signum();
+                    if delta[1].abs() == 1 {
+                        positions[i][1] += delta[1].signum();
+                    }
+                }
+                if delta[1].abs() == 2 {
+                    positions[i][1] += delta[1].signum();
+                    if delta[0].abs() == 1 {
+                        positions[i][0] += delta[0].signum();
+                    }
+                }
+            }
+            seen.insert(positions[NUM_SEGMENTS-1].clone());
+        }
+    }
+
+    println!("{}", seen.len());
+
+    
+}
diff --git a/09/test-1.txt b/09/test-1.txt
new file mode 100644
index 0000000..9874df2
--- /dev/null
+++ b/09/test-1.txt
@@ -0,0 +1,8 @@
+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2
diff --git a/09/test-2.txt b/09/test-2.txt
new file mode 100644
index 0000000..60bd43b
--- /dev/null
+++ b/09/test-2.txt
@@ -0,0 +1,8 @@
+R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20