Complete day 1

day-1/.gitignore

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+/target

day-1/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day-1"
+version = "0.1.0"
+dependencies = [
+ "indoc",
+ "itertools",
+]
+
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+dependencies = [
+ "indoc-impl",
+ "proc-macro-hack",
+]
+
+[[package]]
+name = "indoc-impl"
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+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "unindent",
+]
+
+[[package]]
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+ "either",
+]
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+[[package]]
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+ "unicode-xid",
+]
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+dependencies = [
+ "proc-macro2",
+]
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
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day-1/Cargo.toml

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+[package]
+name = "day-1"
+version = "0.1.0"
+authors = ["Tristan Daniël Maat <tm@tlater.net>"]
+edition = "2018"
+
+[dependencies]
+indoc = "0.3"
+itertools = "0.9"

day-1/input

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+1500
+1635
+1845
+1645
+1999
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day-1/src/main.rs

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+use std::fs;
+
+use itertools::Itertools;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("input")?;
+    let input = parse_number_list(input)?;
+    let numbers = find_2020_numbers(input, 3)?;
+    println!("{}", numbers.iter().product::<u32>());
+    Ok(())
+}
+
+fn parse_number_list(input: String) -> Result<Vec<u32>, std::num::ParseIntError> {
+    input.lines().map(|line| line.parse::<u32>()).collect()
+}
+
+fn find_2020_numbers(input: Vec<u32>, sum_number: usize) -> Result<Vec<u32>, String> {
+    input
+        .into_iter()
+        .combinations(sum_number)
+        .find(|i| i.iter().sum::<u32>() == 2020)
+        .ok_or("Could not find 2020.".to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+
+    #[test]
+    fn test_first_example() -> Result<(), Box<dyn std::error::Error>> {
+        let example = indoc!(
+            "
+            1721
+            979
+            366
+            299
+            675
+            1456
+        "
+        );
+
+        let example = parse_number_list(example.to_string())?;
+        let numbers = find_2020_numbers(example, 2)?;
+
+        assert_eq!(numbers.iter().product::<u32>(), 514579);
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_second_example() -> Result<(), Box<dyn std::error::Error>> {
+        let example = indoc!(
+            "
+            1721
+            979
+            366
+            299
+            675
+            1456
+        "
+        );
+
+        let example = parse_number_list(example.to_string())?;
+        let numbers = find_2020_numbers(example, 3)?;
+
+        assert_eq!(numbers.iter().to_owned().product::<u32>(), 241861950);
+
+        Ok(())
+    }
+}