day 12 solutions

Signed-off-by: Stephen Waits <swaits@amazon.com>

src/day12.rs

@@ -0,0 +1,100 @@
+// ==== day 12
+
+use crate::utils;
+use anyhow::Result;
+use std::mem;
+
+fn navigate(data: &str) -> usize {
+    let mut heading = 90;
+    let (mut pos_n, mut pos_e) = (0, 0);
+    data.lines().for_each(|l| {
+        let dir = &l[0..1];
+        let dist = &l[1..].parse::<i64>().expect("int parse error");
+
+        match dir {
+            "N" => pos_n += dist,
+            "S" => pos_n -= dist,
+            "E" => pos_e += dist,
+            "W" => pos_e -= dist,
+            "L" => heading = (heading + 360 - dist) % 360,
+            "R" => heading = (heading + dist) % 360,
+            "F" => match heading {
+                0 => pos_n += dist,
+                90 => pos_e += dist,
+                180 => pos_n -= dist,
+                270 => pos_e -= dist,
+                360 => pos_n += dist,
+                _ => panic!("non cardinal heading!"),
+            },
+            _ => panic!("bad direction!"),
+        }
+    });
+
+    (pos_n.abs() + pos_e.abs()) as usize
+}
+
+fn navigate2(data: &str) -> usize {
+    let (mut wpt_n, mut wpt_e) = (1, 10);
+    let (mut ship_n, mut ship_e) = (0, 0);
+    data.lines().for_each(|l| {
+        let dir = &l[0..1];
+        let dist = &l[1..].parse::<i64>().expect("int parse error");
+
+        match dir {
+            "N" => wpt_n += dist,
+            "S" => wpt_n -= dist,
+            "E" => wpt_e += dist,
+            "W" => wpt_e -= dist,
+            "L" => match dist {
+                270 => {
+                    wpt_e = -wpt_e;
+                    mem::swap(&mut wpt_n, &mut wpt_e);
+                }
+                180 => {
+                    wpt_n = -wpt_n;
+                    wpt_e = -wpt_e;
+                }
+                90 => {
+                    wpt_n = -wpt_n;
+                    mem::swap(&mut wpt_n, &mut wpt_e);
+                }
+                _ => panic!("bad direction!"),
+            },
+            "R" => match dist {
+                90 => {
+                    wpt_e = -wpt_e;
+                    mem::swap(&mut wpt_n, &mut wpt_e);
+                }
+                180 => {
+                    wpt_n = -wpt_n;
+                    wpt_e = -wpt_e;
+                }
+                270 => {
+                    wpt_n = -wpt_n;
+                    mem::swap(&mut wpt_n, &mut wpt_e);
+                }
+                _ => panic!("bad direction!"),
+            },
+            "F" => {
+                ship_n += dist * wpt_n;
+                ship_e += dist * wpt_e;
+            }
+            _ => panic!("bad direction!"),
+        }
+    });
+
+    (ship_n.abs() + ship_e.abs()) as usize
+}
+
+// main
+pub fn run() -> Result<(usize, usize)> {
+    let data = utils::read_file("data/input-12.txt")?;
+    let answers = utils::read_i64s("data/output-12.txt")?;
+
+    let p1 = navigate(&data);
+    let p2 = navigate2(&data);
+
+    assert_eq!(p1, answers[0] as usize);
+    assert_eq!(p2, answers[1] as usize);
+    Ok((p1, p2))
+}

src/main.rs

@@ -11,6 +11,7 @@ mod day08;
 mod day09;
 mod day10;
 mod day11;
+mod day12;
 mod utils;
 
 // TODO
@@ -35,5 +36,6 @@ fn main() -> Result<()> {
     println!("Day 09: {:?}", day09::run()?);
     println!("Day 10: {:?}", day10::run()?);
     println!("Day 11: {:?}", day11::run()?);
+    println!("Day 12: {:?}", day12::run()?);
     Ok(())
 }