day 9

day9/src/main.rs

@@ -0,0 +1,38 @@
+use std::fs::read_to_string;
+
+fn get_numbers_in_line_iter<T: std::str::FromStr>(str: &str) -> impl Iterator<Item=T> + '_ {
+    str.split_whitespace().filter_map(|substr| substr.parse::<T>().ok())
+}
+
+fn main() {
+    let mut sum1 = 0;
+    let mut sum2 = 0;
+    let mut working_vec: Vec<i32> = Vec::new();
+    for line in read_to_string("input.txt").unwrap().lines() {
+        working_vec.extend(get_numbers_in_line_iter::<i32>(line));
+        let original_length = working_vec.len();
+        let mut sequence_length = working_vec.len() - 1;
+        while sequence_length > 0 {
+            let mut all_zeros = true;
+            working_vec.push(working_vec[0]);
+            for i in 0..sequence_length {
+                working_vec[i] = working_vec[i + 1] - working_vec[i];
+                if working_vec[i] != 0 {
+                    all_zeros = false;
+                }
+            }
+            if all_zeros {
+                break;
+            }
+            sequence_length -= 1;
+        }
+        let extrapolated1 = working_vec[sequence_length..original_length].iter().sum::<i32>();
+        let extrapolated2 = working_vec[original_length..].iter().rev().fold(
+            0, |acc, x| x - acc);
+        sum1 += extrapolated1;
+        sum2 += extrapolated2;
+        working_vec.clear();
+    }
+    println!("Sum1: {}", sum1);
+    println!("Sum2: {}", sum2);
+}