Day 09 Part 2 Complete

src/solutions/day09.rs

@@ -5,16 +5,18 @@ pub struct Day09 {}
 impl Solution for Day09 {
     fn part1(
         &self,
-        _input: &mut Vec<String>,
+        input: &mut Vec<String>,
     ) -> Result<Box<dyn std::fmt::Display + Sync>, Box<dyn std::error::Error>> {
-        Ok(Box::new("Ready"))
+        let series_collection = self.get_series(input)?;
+        Ok(Box::new(self.sum_extrapolated(&series_collection, true)?))
     }
 
     fn part2(
         &self,
-        _input: &mut Vec<String>,
+        input: &mut Vec<String>,
     ) -> Result<Box<dyn std::fmt::Display + Sync>, Box<dyn std::error::Error>> {
-        Ok(Box::new("Ready"))
+        let series_collection = self.get_series(input)?;
+        Ok(Box::new(self.sum_extrapolated(&series_collection, false)?))
     }
 
     fn get_day(&self) -> u8 {
@@ -22,7 +24,77 @@ impl Solution for Day09 {
     }
 }
 
-impl Day09 {}
+impl Day09 {
+    /// Takes a vec of strings and returns a Vec of series of numbers
+    fn get_series(&self, input: &Vec<String>) -> Result<Vec<Vec<i32>>, Box<dyn std::error::Error>> {
+        let mut series = vec![];
+        for s in input.iter() {
+            series.push(
+                s.split_whitespace()
+                    .map(|n| n.parse::<i32>().unwrap())
+                    .collect(),
+            );
+        }
+        Ok(series)
+    }
+
+    /// Returns the sum ov extrapolated values either to the left or the right of the initial series
+    fn sum_extrapolated(
+        &self,
+        series_collection: &Vec<Vec<i32>>,
+        forwards: bool,
+    ) -> Result<i32, Box<dyn std::error::Error>> {
+        let mut ans = 0i32;
+
+        for series in series_collection {
+            let mut differences = vec![series.clone()];
+
+            // Keep finding differences until we have a consistent difference of 0
+            while differences
+                .last()
+                .unwrap()
+                .iter()
+                .map(|v| v.abs())
+                .sum::<i32>()
+                != 0i32
+            {
+                differences.push(
+                    differences
+                        .last()
+                        .unwrap()
+                        .windows(2)
+                        .map(|w| w[1] - w[0])
+                        .collect::<Vec<i32>>(),
+                );
+            }
+
+            if forwards {
+                // Sum all of the last values in each row to get next num
+                ans += differences
+                    .iter()
+                    .map(|s| *s.last().unwrap())
+                    .collect::<Vec<i32>>()
+                    .iter()
+                    .sum::<i32>();
+            } else {
+                // Scale backwards down the heap to find the previous number in each sequence
+                let mut next = 0i32;
+                differences
+                    .iter()
+                    .rev()
+                    .map(|s| *s.first().unwrap())
+                    .collect::<Vec<i32>>()
+                    .iter()
+                    .for_each(|v| {
+                        next = v - next;
+                    });
+                ans += next;
+            }
+        }
+
+        Ok(ans)
+    }
+}
 
 /// Test from puzzle input
 #[cfg(test)]
@@ -44,7 +116,7 @@ mod test {
             .unwrap()
             .to_string();
 
-        assert_eq!(answer, "Ready");
+        assert_eq!(answer, "114");
     }
 
     #[test]
@@ -61,6 +133,6 @@ mod test {
             .unwrap()
             .to_string();
 
-        assert_eq!(answer, "Ready");
+        assert_eq!(answer, "2");
     }
 }