Part 09

src/bin/part09.rs

@@ -0,0 +1,75 @@
+use std::time;
+
+fn main() {
+    let t1 = time::Instant::now();
+
+    let data = load_input();
+
+    let d1 = t1.elapsed();
+    println!("Loading: {:?}", d1);
+    let t2 = time::Instant::now();
+
+    let sum1 = data.iter().map(|d| extrapolate_next_value(&d)).sum::<i32>();
+    let sum2 = data.iter().map(|d| extrapolate_previous_value(&d)).sum::<i32>();
+
+    let d2 = t2.elapsed();
+    println!("Summing: {:?}", d2);
+    println!("Total: {:?}", d1 + d2);
+    println!("Sum1: {}", sum1);
+    println!("Sum2: {}", sum2);
+
+    assert_eq!(sum1, 1584748274);
+    assert_eq!(sum2, 1026);
+}
+
+fn extrapolate_next_value(series: &[i32]) -> i32 {
+    let differences = forward_differences(series);
+    let mut next_value = *series.last().unwrap();
+
+    next_value += differences.iter().skip(1).map(|d| d.last().unwrap()).sum::<i32>();
+
+    // for diff in differences.iter().skip(1) {
+    //     next_value += diff.last().unwrap();
+    // }
+
+    next_value
+}
+
+fn extrapolate_previous_value(series: &[i32]) -> i32 {
+    let differences = forward_differences(series);
+    let mut previous_value = *series.first().unwrap();
+
+    for (i, diff) in differences.iter().skip(1).enumerate() {
+        if i % 2 == 0 {
+            previous_value -= diff[0];
+        } else {
+            previous_value += diff[0];
+        }
+    }
+
+    previous_value
+}
+
+fn forward_differences(series: &[i32]) -> Vec<Vec<i32>> {
+    let mut differences = vec![series.to_vec()];
+    
+    while differences.last().unwrap().iter().any(|d| *d != 0) {
+        let last = differences.last().unwrap();
+        let next = last.windows(2).map(|w| w[1] - w[0]).collect();
+        differences.push(next);
+    }
+
+    differences
+}
+
+fn load_input() -> Vec<Vec<i32>> {
+    let data = std::fs::read_to_string("src/bin/part09.txt")
+        .expect("Could not read file")
+        .lines()
+        .map(|l| {
+            l.split_whitespace().map(|s| s.parse::<i32>().unwrap()).collect::<Vec<_>>()
+        })
+        .collect::<Vec<_>>();
+
+    data
+}