solve Day09 in Rust

Day09/rust/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "rust"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

Day09/rust/src/main.rs

@@ -0,0 +1,67 @@
+use std::fs::File;
+use std::io::{self, BufRead, BufReader};
+use std::path::Path;
+
+fn generate_difference_table(history: &[i32]) -> Vec<Vec<i32>> {
+    // Generates a difference table for a given history
+    let mut table: Vec<Vec<i32>> = vec![history.to_vec()];
+    while !table.last().unwrap().iter().all(|&x| x == 0) {
+        let next_row: Vec<i32> = table
+            .last()
+            .unwrap()
+            .windows(2)
+            .map(|pair| pair[1] - pair[0])
+            .collect();
+        table.push(next_row);
+    }
+    table
+}
+
+fn extrapolate_previous_value(table: &mut Vec<Vec<i32>>) -> i32 {
+    // Extrapolates the previous value from the difference table
+    for i in (0..table.len() - 1).rev() {
+        let diff = table[i][0] - table[i + 1][0];
+        table[i].insert(0, diff);
+    }
+    table[0][0]
+}
+
+fn solve_puzzle(filename: &str) -> Result<i32, io::Error> {
+    // Solves the puzzle by reading histories from the file and summing their extrapolated previous values
+    let path = Path::new(filename);
+    let file = File::open(path)?;
+    let reader = BufReader::new(file);
+
+    let mut total = 0;
+    for line in reader.lines() {
+        let line = line?;
+        if line.trim().is_empty() {
+            continue;
+        }
+        let history: Vec<i32> = line.split_whitespace().map(|s| s.parse().unwrap()).collect();
+        let mut diff_table = generate_difference_table(&history);
+        let prev_value = extrapolate_previous_value(&mut diff_table);
+        total += prev_value;
+    }
+
+    Ok(total)
+}
+
+fn test() -> Result<(), io::Error> {
+    // Runs the test using the test.txt file and asserts the expected outcome
+    let expected = 2; // Expected result from the test data for the second part
+    let result = solve_puzzle("../test.txt")?;
+    assert_eq!(result, expected, "Test failed: Expected {}, got {}", expected, result);
+    println!("Test passed successfully.");
+    Ok(())
+}
+
+fn main() -> Result<(), io::Error> {
+    // Main function to run the test and then solve the puzzle
+    println!("Running test for the second part...");
+    test()?;
+    println!("Test completed. Solving the puzzle for the second part...");
+    let result = solve_puzzle("../input.txt")?;
+    println!("Puzzle result for the second part: {}", result);
+    Ok(())
+}