2016/01

2016/01/src/main.rs

@@ -1,3 +1,90 @@
+use std::io::{self, Read};
+use std::collections::HashSet;
+
+
 fn main() {
-    println!("Hello, world!");
+    let mut buffer = String::new();
+
+    io::stdin().read_to_string(&mut buffer).unwrap();
+
+    let (end, real) = follow_instructions(&buffer);
+
+    if let Some((x, y)) = end {
+        println!("end position: x={}, y={}", x, y);
+    }
+    if let Some((x, y)) = real {
+        println!("real position: x={}, y={}", x, y);
+    }
+}
+
+fn follow_instructions(input: &str) -> (Option<(i32, i32)>, Option<(i32, i32)>) {
+    let instructions = input
+        .split(",")
+        .map(|x| x.trim())
+        .map(|x| x.split_at(1))
+        .map(|(x, y)| (x, y.parse::<i32>().unwrap()));
+
+    let mut x = 0;
+    let mut y = 0;
+
+    let mut delta = (0, 1);
+
+    let mut visited = HashSet::new();
+    let mut position: Option<(i32, i32)> = None;
+
+    for (direction, steps) in instructions {
+        delta = match direction {
+            "R" => (delta.1, delta.0 * -1),
+            "L" => (delta.1 * -1, delta.0),
+            _   => delta,
+        };
+
+        for _ in 0..steps {
+            x += delta.0;
+            y += delta.1;
+
+            if position.is_none() {
+                if visited.contains(&(x, y)) {
+                    position = Some((x, y));
+                } else {
+                    visited.insert((x, y));
+                }
+            }
+        }
+    }
+
+    (Some((x, y)), position)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::follow_instructions;
+
+    #[test]
+    fn example_01() {
+        let input = "R2, L3";
+
+        assert_eq!((Some((2, 3)), None), follow_instructions(input));
+    }
+
+    #[test]
+    fn example_02() {
+        let input = "R2, R2, R2";
+
+        assert_eq!((Some((0, -2)), None), follow_instructions(input));
+    }
+
+    #[test]
+    fn example_03() {
+        let input = "R5, L5, R5, R3";
+
+        assert_eq!((Some((10, 2)), None), follow_instructions(input));
+    }
+
+    #[test]
+    fn example_04() {
+        let input = "R8, R4, R4, R8";
+
+        assert_eq!((Some((4, 4)), Some((4, 0))), follow_instructions(input));
+    }
 }