day 12

had a lot of issues with this one. I understood i needed dijkstra's from
the start because the second part would probably increase the complexity,
but I did not read the question enough and did not realize that we could
go down by any amount, only increases in elevation were limited. This
resulted in a lot of time being wasted on debug code to print the grid.

day_12/src/main.rs

@@ -1,3 +1,199 @@
-fn main() {
-    println!("Hello, world!");
+use std::{
+    cmp::Ordering,
+    collections::{BinaryHeap, HashSet},
+    fs::read_to_string,
+};
+
+const PATH: &str = "src/input";
+
+fn get_dim(input: &[u8]) -> (usize, usize) {
+    let height = input.iter().filter(|c| **c == b'\n').count() + 1;
+    let width = input.iter().position(|c| *c == b'\n').unwrap();
+    (height, width)
+}
+
+fn get_start(input: &[u8]) -> usize {
+    get_char(input, b'S')
+}
+fn get_end(input: &[u8]) -> usize {
+    get_char(input, b'E')
+}
+
+fn get_char(input: &[u8], needle: u8) -> usize {
+    let i = input.iter().position(|c| *c == needle).unwrap();
+    // (i % width, i / width)
+    i
+}
+
+// COPIED FROM RUST DOCS
+// https://doc.rust-lang.org/std/collections/binary_heap/index.html
+#[derive(Copy, Clone, Eq, PartialEq)]
+struct Vert {
+    distance: usize,
+    position: usize,
+}
+
+// The priority queue depends on `Ord`.
+// Explicitly implement the trait so the queue becomes a min-heap
+// instead of a max-heap.
+impl Ord for Vert {
+    fn cmp(&self, other: &Self) -> Ordering {
+        // Notice that the we flip the ordering on costs.
+        // In case of a tie we compare positions - this step is necessary
+        // to make implementations of `PartialEq` and `Ord` consistent.
+        other
+            .distance
+            .cmp(&self.distance)
+            .then_with(|| self.position.cmp(&other.position))
+    }
+}
+
+// `PartialOrd` needs to be implemented as well.
+impl PartialOrd for Vert {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+// END
+
+fn main() {
+    let binding = read_to_string(PATH).expect("Error reading file");
+    assert!(binding.is_ascii());
+    let (b_height, b_width) = get_dim(binding.trim().as_bytes());
+
+    let binding = binding.replace('\n', "");
+    let data = binding.trim().as_bytes();
+
+    macro_rules! ij {
+        ($index: expr) => {
+            ($index % b_width, $index / b_width)
+        };
+    }
+
+    macro_rules! linear {
+        ($i:expr, $j:expr) => {
+            $i + $j * b_width
+        };
+    }
+
+    println!("BOARD SIZE {} {}", b_width, b_height);
+    let start = get_start(data);
+    println!("start {} {}", ij!(start).0, ij!(start).1);
+    let end = get_end(data);
+    println!("end {} {}", ij!(end).0, ij!(end).1);
+
+    let mut previous = (0..b_width * b_height)
+        .map(|_| None)
+        .collect::<Vec<Option<usize>>>();
+    let mut distances = (0..b_width * b_height)
+        .map(|_| usize::MAX)
+        .collect::<Vec<usize>>();
+    distances[end] = 0;
+    let mut visited = (0..b_width * b_height)
+        .map(|_| false)
+        .collect::<Vec<bool>>();
+    let mut vertex_q = (0..b_width * b_height)
+        .map(|v| Vert {
+            position: v,
+            distance: distances[v],
+        })
+        .collect::<BinaryHeap<Vert>>();
+    let mut frontier_scanned = Vec::<usize>::new();
+
+    while let Some(u) = vertex_q.pop() {
+        // GET ADJACENT VERTEXES
+        if visited[u.position] {
+            continue;
+        }
+        let u_tuple = ij!(u.position);
+        let mut adjacent = Vec::<usize>::new();
+        if u_tuple.0 >= 1 {
+            adjacent.push(linear!(u_tuple.0 - 1, u_tuple.1));
+        }
+        if u_tuple.0 < b_width - 1 {
+            adjacent.push(linear!(u_tuple.0 + 1, u_tuple.1));
+        }
+        if u_tuple.1 >= 1 {
+            adjacent.push(linear!(u_tuple.0, u_tuple.1 - 1));
+        }
+        if u_tuple.1 < b_height - 1 {
+            adjacent.push(linear!(u_tuple.0, u_tuple.1 + 1));
+        }
+        // END
+        // println!(
+        //     "@ {} {} ADJ TO {}",
+        //     u.position % b_width,
+        //     u.position / b_width,
+        //     adjacent.len()
+        // );
+        for v in &adjacent {
+            let v = *v;
+            // UNIFORM STEP COST OF 1
+            let alt_path = if data[u.position] != b'E' && data[u.position].abs_diff(data[v]) <= 1
+                || data[u.position] != b'E' && data[u.position] < data[v]
+                || data[u.position] == b'E' && data[v] == b'z'
+                || data[u.position] == b'a' && data[v] == b'S'
+            {
+                frontier_scanned.push(v);
+                distances[u.position].saturating_add(1)
+            } else {
+                usize::MAX
+            };
+            if alt_path < distances[v] {
+                // println!(
+                //     "ADJACENT TO ({},{}) : ({},{}) {} {} {}",
+                //     u.position % b_width,
+                //     u.position / b_width,
+                //     v % b_width,
+                //     v / b_width,
+                //     data[u.position] as char,
+                //     data[v] as char,
+                //     data[u.position].abs_diff(data[v])
+                // );
+                distances[v] = alt_path;
+                previous[v] = Some(u.position);
+                vertex_q.push(Vert {
+                    distance: alt_path,
+                    position: v,
+                })
+            }
+            visited[u.position] = true;
+        }
+    }
+
+    //PRINT GRID
+    let mut shortest_path = HashSet::<usize>::new();
+    let mut x = start;
+    shortest_path.insert(start);
+    while previous[x].is_some() {
+        shortest_path.insert(previous[x].unwrap());
+        x = previous[x].unwrap();
+    }
+
+    for j in 0..b_height {
+        for i in 0..b_width {
+            let index = i + j * b_width;
+            if shortest_path.contains(&(index)) {
+                print!("\x1b[31m{}\x1b[0m", data[index] as char);
+            } else if visited[index] {
+                print!("{}", data[index] as char);
+            } else if frontier_scanned.contains(&(index)) {
+                print!("\x1b[43m{}\x1b[0m", data[index] as char);
+            } else {
+                print!("\x1b[93m{}\x1b[0m", data[index] as char);
+            }
+        }
+        println!();
+    }
+    //END
+    println!("PART 1 {}", distances[start]);
+
+    let a_ends = data
+        .iter()
+        .enumerate()
+        .filter(|(_, &c)| c == b'a')
+        .map(|(i, _)| distances[i])
+        .min()
+        .unwrap();
+    println!("PART 2 {}", a_ends);
 }