finished day 3

src/bin/3.rs

@@ -0,0 +1,53 @@
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+fn traverse(xslope: usize, yslope: usize, data: &Vec<Vec<bool>>) -> i64 {
+    let mut x = 0;
+    let mut y = 0;
+    let mut count = 0;
+
+    loop {
+        y += yslope;
+        x += xslope;
+        let row = data.get(y).unwrap();
+        if x >= row.len() {
+            x = x % row.len();
+        }
+        if row[x] {
+            count += 1;
+        }
+        if y == data.len() - 1 {
+            return count;
+        }
+    }
+}
+
+fn main() -> anyhow::Result<()> {
+    let file = File::open("3.input")?;
+    let reader = BufReader::new(file);
+
+    let mut data: Vec<Vec<bool>> = Vec::new();
+
+    for line in reader.lines() {
+        data.push(Vec::new());
+        let current_line = data.last_mut().unwrap();
+        for c in line?.chars() {
+            match c {
+                '#' => current_line.push(true),
+                '.' => current_line.push(false),
+                '\n' => (),
+                _ => panic!("unexpected input"),
+            }
+        }
+    }
+
+    println!("Count is {}", traverse(3, 1, &data));
+    let second = traverse(1, 1, &data) * 
+        traverse(3, 1, &data) * 
+        traverse(5, 1, &data) * 
+        traverse(7, 1, &data) * 
+        traverse(1, 2, &data);
+    println!("Second count is {}", second);
+
+    Ok(())
+}