Day 8 part 1

inputs/8_test.txt

@@ -0,0 +1 @@
+2 3 0 3 10 11 12 1 1 0 1 99 2 1 1 2

src/day8.rs

@@ -0,0 +1,60 @@
+use std::error::Error;
+use std::fs;
+use std::result;
+
+type Result<T> = result::Result<T, Box<Error>>;
+
+const INPUT: &str = "inputs/8.txt";
+
+pub fn solve_part1() -> Result<u32> {
+    let license = read_license(INPUT)?;
+    Ok(sum_metadata(&license, 0, 0).0)
+}
+
+fn read_license(filename: &str) -> Result<Vec<u32>> {
+    let license = fs::read_to_string(filename)?;
+    let license = license.trim();
+    Ok(license
+        .split(' ')
+        .map(|num| num.parse().unwrap())
+        .collect())
+}
+
+fn sum_metadata(license: &[u32], mut index: usize, mut sum_acc: u32) -> (u32, usize) {
+    let num_children = license[index];
+    let num_metadata = license[index + 1];
+    index += 2;
+    if num_children != 0 {
+        for _ in 0..num_children {
+            let (child_sum_acc, child_index) = sum_metadata(license, index, sum_acc);
+            sum_acc = child_sum_acc;
+            index = child_index;
+        }
+    }
+    if num_metadata != 0 {
+        let sum: u32 = license[index..index + num_metadata as usize].iter().sum();
+        index += num_metadata as usize;
+        sum_acc += sum;
+    }
+    (sum_acc, index)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "inputs/8_test.txt";
+    fn test_license() -> Vec<u32> {
+        vec![2, 3, 0, 3, 10, 11, 12, 1, 1, 0, 1, 99, 2, 1, 1, 2]
+    }
+
+    #[test]
+    fn reads_license_file() {
+        assert_eq!(read_license(TEST_INPUT).unwrap(), test_license());
+    }
+
+    #[test]
+    fn sums_license_metadata() {
+        assert_eq!(sum_metadata(&test_license(), 0, 0).0, 138);
+    }
+}

src/main.rs

@@ -10,6 +10,7 @@ mod day4;
 mod day5;
 mod day6;
 mod day7;
+mod day8;
 
 fn main() {
     // println!("Day 1:");
@@ -30,7 +31,9 @@ fn main() {
     // println!("Day 6:");
     // println!("{}", day6::solve_part1().unwrap());
     // println!("{}", day6::solve_part2().unwrap());
-    println!("Day 7:");
+    // println!("Day 7:");
     // println!("{}", day7::solve_part1().unwrap());
-    println!("{}", day7::solve_part2().unwrap());
+    // println!("{}", day7::solve_part2().unwrap());
+    println!("Day 8:");
+    println!("{}", day8::solve_part1().unwrap());
 }