2023-09: Solve part 2

src/year_2023/day_09_mirage_maintenance/common.rs

@@ -0,0 +1,11 @@
+pub fn parse_line(s: &str) -> Vec<i32> {
+    s.split_whitespace().map(|x| x.parse().unwrap()).collect()
+}
+
+pub fn get_differences(nums: Vec<i32>) -> Vec<i32> {
+    nums.windows(2).map(|w| w[1] - w[0]).collect()
+}
+
+pub fn all_zeros(nums: Vec<i32>) -> bool {
+    nums.iter().all(|&x| x == 0)
+}

src/year_2023/day_09_mirage_maintenance/mod.rs

@@ -1,5 +1,6 @@
 pub mod part_one;
-// pub mod part_two;
+pub mod part_two;
+pub mod common;
 
 use crate::utils::solution::Solution;
 use crate::utils::input_reader;
@@ -8,16 +9,12 @@ use crate::utils::input_reader;
 pub struct Day9Solution;
 
 impl Solution for Day9Solution {
+
     fn part_one(&self) -> String {
-        // Implementation for part one of day 1
-        // ...
         input_reader::read_input_file("input/2023/day_09/input.txt", part_one::part_one)
     }
 
     fn part_two(&self) -> String {
-        // Implementation for part two of day 1
-        // ...
-        String::from("Not implemented")
-        // part_two::part_two()
+        input_reader::read_input_file("input/2023/day_09/input.txt", part_two::part_two)
     }
 }

src/year_2023/day_09_mirage_maintenance/part_one.rs

@@ -1,3 +1,5 @@
+use super::common::{parse_line, get_differences, all_zeros};
+
 pub fn part_one(input_lines: Vec<String>) -> String {
     let mut result: i32 = 0;
 
@@ -19,16 +21,4 @@ pub fn part_one(input_lines: Vec<String>) -> String {
     }
 
     result.to_string()
-}
-
-fn parse_line(s: &str) -> Vec<i32> {
-    s.split_whitespace().map(|x| x.parse().unwrap()).collect()
-}
-
-fn get_differences(nums: Vec<i32>) -> Vec<i32> {
-    nums.windows(2).map(|w| w[1] - w[0]).collect()
-}
-
-fn all_zeros(nums: Vec<i32>) -> bool {
-    nums.iter().all(|&x| x == 0)
 }

src/year_2023/day_09_mirage_maintenance/part_two.rs

@@ -0,0 +1,29 @@
+use super::common::{parse_line, get_differences, all_zeros};
+
+pub fn part_two(input_lines: Vec<String>) -> String {
+    let mut result: i32 = 0;
+
+    for line in input_lines {
+        let nums = parse_line(&line);
+
+        let mut first: Vec<i32> = Vec::new();
+        first.push(nums.first().unwrap().clone());
+
+        let mut diffs = get_differences(nums.clone());
+        first.push(diffs.first().unwrap().clone());
+
+        while !all_zeros(diffs.clone()) {
+            diffs = get_differences(diffs.clone());
+            first.push(diffs.first().unwrap().clone());
+        }
+
+        first.reverse();
+
+        let mut res = 0;        
+        res = first.iter().fold(res, |acc, &x| x - acc);
+
+        result += res;
+    }
+
+    result.to_string()
+}