day 09

aoc2023/src/day09.rs

@@ -1,13 +1,51 @@
+use std::iter::zip;
 use shared::{Solution, Answer};
 
 pub struct Day09;
 
 impl Solution for Day09 {
     fn part_1(&self, input: &str) -> Answer {
-        Answer::Unimplemented
+        let lines = input.split("\n")
+            .map(|l| l.split_whitespace().map(|x| x.parse::<i64>().unwrap()).collect()
+            ).collect::<Vec<Vec<i64>>>();
+
+        Answer::from(
+            lines.iter().map(solve1).sum::<i64>()
+        )
     }
 
     fn part_2(&self, input: &str) -> Answer {
-        Answer::Unimplemented
+        let lines = input.split("\n")
+            .map(|l| l.split_whitespace().map(|x| x.parse::<i64>().unwrap()).collect()
+            ).collect::<Vec<Vec<i64>>>();
+
+        Answer::from(
+            lines.iter().map(solve2).sum::<i64>()
+        )
     }
 }
+
+fn solve1(seq: &Vec<i64>) -> i64 {
+    if seq.iter().all(|x| *x==0) {
+        return 0
+    }
+
+    let diffs = zip(seq, seq.iter().skip(1))
+        .map(|(a, b)| b - a )
+        .collect();
+
+    return seq.last().unwrap() + solve1(&diffs)
+}
+
+fn solve2(seq: &Vec<i64>) -> i64 {
+    if seq.iter().all(|x| *x==0) {
+        return 0
+    }
+
+    let diffs = zip(seq, seq.iter().skip(1))
+        .map(|(a, b)| b - a )
+        .collect();
+
+    return seq.first().unwrap() - solve2(&diffs)
+}
+