Implement day 1 2018.

We've started.

2018/src/day01.rs

@@ -0,0 +1,79 @@
+use std::collections::HashSet;
+use std::io;
+use std::io::prelude::*;
+use common;
+
+pub struct Day01 {}
+
+impl Day01 {
+    pub fn new() -> Day01 {
+        Day01 {}
+    }
+}
+
+impl common::Solution for Day01 {
+    fn part1(&mut self, input: &mut io::Read) -> String {
+        let reader = io::BufReader::new(input);
+
+        let sum: i32 = reader.lines()
+            .map(|x| x.unwrap().parse::<i32>().unwrap())
+            .sum();
+
+        format!("{}", sum)
+    }
+
+    fn part2(&mut self, input: &mut io::Read) -> String {
+        let reader = io::BufReader::new(input);
+        let mut freqs = HashSet::new();
+        freqs.insert(0);
+
+        let mut sum = 0;
+        let nums: Vec<i32> = reader.lines()
+            .map(|x| x.unwrap().parse().unwrap())
+            .collect();
+        loop {
+            for amount in &nums {
+                sum += amount;
+                if freqs.contains(&sum) {
+                    return format!("{}", sum);
+                } else {
+                    freqs.insert(sum);
+                }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use common::Solution;
+
+    #[test]
+    fn samples_part1() {
+        let mut instance = Day01::new();
+        let sample1 = "+1\n+1\n+1";
+        let sample2 = "+1\n+1\n-2";
+        let sample3 = "-1\n-2\n-3";
+
+        assert_eq!("3", instance.part1(&mut sample1.as_bytes()));
+        assert_eq!("0", instance.part1(&mut sample2.as_bytes()));
+        assert_eq!("-6", instance.part1(&mut sample3.as_bytes()));
+    }
+
+    #[test]
+    fn samples_part2() {
+        let mut instance = Day01::new();
+        let sample1 = "+1\n-1";
+        let sample2 = "+3\n+3\n+4\n-2\n-4";
+        let sample3 = "-6\n+3\n+8\n+5\n-6";
+        let sample4 = "+7\n+7\n-2\n-7\n-4";
+
+        assert_eq!("0", instance.part2(&mut sample1.as_bytes()));
+        assert_eq!("10", instance.part2(&mut sample2.as_bytes()));
+        assert_eq!("5", instance.part2(&mut sample3.as_bytes()));
+        assert_eq!("14", instance.part2(&mut sample4.as_bytes()));
+    }
+
+
+}