feat: day1

Signed-off-by: Louis Vallat <louis@louis-vallat.xyz>

.gitignore

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+target
+Cargo.lock

.gitlab-ci.yml

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+default:
+  image: rust
+
+stages:
+  - build
+
+day-1:
+  stage: build
+  script:
+    - cd day1; cargo run --release ./input
+

day1/Cargo.toml

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+[package]
+name = "day1"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day1/src/main.rs

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+use std::{fs, env};
+
+fn read_input(path: &str) -> String {
+    return fs::read_to_string(path).expect("Cannot read file.");
+}
+
+fn parse_input(s: &str) -> Vec<Vec<i32>> {
+    let mut ret = vec![];
+    let mut buffer = vec![];
+    for l in s.lines() {
+        if l.is_empty() {
+            ret.push(buffer.clone());
+            buffer.clear();
+        } else {
+            buffer.push(l.parse::<i32>().unwrap())
+        }
+    }
+    return ret;
+}
+
+fn sort_and_sum(input: &Vec<Vec<i32>>) -> Vec<i32> {
+    let mut summed = input.iter()
+        .map(|i| i.iter().sum()).collect::<Vec<i32>>();
+    summed.sort();
+    return summed;
+}
+
+fn sum_of_last_n(sorted: &Vec<i32>, n: usize) -> i32 {
+    return sorted.iter().rev().take(n).sum();
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        println!("[{}]", &arg);
+        let vec_in = parse_input(&read_input(&arg));
+        let sorted = sort_and_sum(&vec_in);
+        println!("\t[Part 1] => Answer is '{}'.", sum_of_last_n(&sorted, 1));
+        println!("\t[Part 2] => Answer is '{}'.", sum_of_last_n(&sorted, 3));
+    }
+}