add day 1 and 2 solutions

day01/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day01"
+version = "0.1.0"

day01/Cargo.toml

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+[package]
+name = "day01"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day01/src/main.rs

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+use std::io::{self, BufRead};
+
+fn main() {
+    let nums: Vec<u64> = io::stdin()
+        .lock()
+        .lines()
+        .map(|line| line.unwrap().parse::<u64>().unwrap())
+        .collect();
+
+    let p1: u64 = nums.iter().map(|&num| mass_to_fuel(num)).sum();
+    let p2: u64 = nums.iter().map(|&num| fuel_for_fuel(num)).sum();
+
+    println!("P1: {}, P2: {}", p1, p2);
+}
+
+fn mass_to_fuel(mass: u64) -> u64 {
+    (mass / 3).saturating_sub(2)
+}
+
+fn fuel_for_fuel(fuel: u64) -> u64 {
+    let mut tot = 0;
+    let mut fuel = fuel;
+
+    while fuel > 0 {
+        fuel = mass_to_fuel(fuel);
+        tot += fuel;
+    }
+
+    tot
+}