Added day 1 code for part 1 and 2

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

.gitignore

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+target
+Cargo.lock

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, collections::BTreeMap};
+
+fn read_input(path: &str) -> String {
+    return fs::read_to_string(path).expect("Cannot read file.");
+}
+
+fn parse_input(s: &str) -> Vec<i32> {
+    return s.split("\n").into_iter().filter_map(|f| f.parse::<i32>().ok()).collect::<Vec<i32>>();
+}
+
+fn get_increase_nb(e: &Vec<i32>) -> i32 {
+    let mut n = 0;
+    for i in 1..e.len() {
+        n += if e[i] > e[i - 1] { 1 } else { 0 };
+    }
+    return n;
+}
+
+fn get_sums(v: &Vec<i32>) -> BTreeMap<usize, i32> {
+    let mut sums = BTreeMap::new();
+    for i in 0..(v.len() - 2) {
+        sums.insert(i, v[i] + v[i + 1] + v[i + 2]);
+    }
+    return sums;
+}
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    for arg in args.iter().skip(1) {
+        let vec_in = parse_input(&read_input(&arg));
+        println!("[{}]", &arg);
+        println!("\t[Part 1] => Answer is '{}'.", get_increase_nb(&vec_in));
+        let map = get_sums(&vec_in).iter().map(|e| e.1.to_owned()).collect::<Vec<i32>>();
+        println!("\t[Part 2] => Answer is '{}'.", get_increase_nb(&map));
+    }
+}
+