From 34bffc49705fb31f947ad0f2f45494dc9472e81b Mon Sep 17 00:00:00 2001
From: Justin Worthe <justin@worthe-it.co.za>
Date: Sun, 1 Dec 2019 09:24:11 +0200
Subject: Day 1

---
 Cargo.lock       |   6 ++++
 inputs/day_1.txt | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 readme.org       |  12 +++++++
 src/bin/day_1.rs |  97 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs      |  11 +++++-
 5 files changed, 225 insertions(+), 1 deletion(-)
 create mode 100644 Cargo.lock
 create mode 100644 inputs/day_1.txt
 create mode 100644 readme.org
 create mode 100644 src/bin/day_1.rs

diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..3719353
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,6 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "advent-of-code-2019"
+version = "0.1.0"
+
diff --git a/inputs/day_1.txt b/inputs/day_1.txt
new file mode 100644
index 0000000..5c720ed
--- /dev/null
+++ b/inputs/day_1.txt
@@ -0,0 +1,100 @@
+66690
+86239
+75191
+140364
+95979
+106923
+95229
+123571
+84764
+89444
+98107
+89062
+109369
+146067
+124760
+76900
+139198
+111441
+74046
+84920
+54397
+143807
+121654
+93863
+73909
+104121
+58485
+119084
+126227
+142078
+79820
+132617
+108430
+98032
+107434
+127307
+105619
+57741
+53468
+63301
+137970
+136780
+80897
+133205
+79159
+89124
+94477
+56714
+143704
+122097
+117335
+108246
+75507
+101459
+101162
+146197
+121884
+66217
+57074
+142903
+140951
+64883
+124556
+67382
+142407
+121778
+57933
+94599
+87426
+143758
+64043
+65678
+90137
+61090
+77315
+102383
+146607
+139290
+85394
+149787
+125611
+106405
+91561
+135739
+54845
+68782
+111175
+61011
+125658
+70751
+85607
+75458
+75419
+124311
+66022
+122784
+129018
+54901
+73788
+108240
diff --git a/readme.org b/readme.org
new file mode 100644
index 0000000..c1923ac
--- /dev/null
+++ b/readme.org
@@ -0,0 +1,12 @@
+* Advent of Code 2019
+
+** Personal challenge
+
+Try to keep the solution pure. Only main can do IO things, like return
+different results when it's called differently. The rest of the
+program should only be pure expressions.
+
+** Optimizations
+
+- Limit the use of statements. Try to use expressions instead, or move
+  the statement out to a function.
diff --git a/src/bin/day_1.rs b/src/bin/day_1.rs
new file mode 100644
index 0000000..7c8f104
--- /dev/null
+++ b/src/bin/day_1.rs
@@ -0,0 +1,97 @@
+use std::io;
+use std::io::prelude::*;
+use std::iter;
+use std::iter::Sum;
+use std::num::ParseIntError;
+use std::ops::Add;
+use std::str::FromStr;
+
+fn main() {
+    let stdin = io::stdin();
+
+    let input = stdin
+        .lock()
+        .lines()
+        .map(|l| l.unwrap().parse::<Module>().unwrap());
+
+    dbg!(fuel_required(input));
+}
+
+// TODO: If this were a nice CLI program, it would probably have a switch to choose between these two rather than doing both?
+fn fuel_required(it: impl Iterator<Item = Module>) -> (Fuel, Fuel) {
+    it.map(|m| {
+        (
+            m.fuel_excluding_fuel_weight(),
+            m.fuel_including_fuel_weight(),
+        )
+    })
+    .fold((Fuel(0), Fuel(0)), |(sum_x, sum_y), (x, y)| {
+        (sum_x + x, sum_y + y)
+    })
+}
+
+struct Module {
+    weight: Weight,
+}
+
+impl FromStr for Module {
+    type Err = ParseIntError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(Module {
+            weight: Weight(s.parse()?),
+        })
+    }
+}
+
+impl Module {
+    fn fuel_excluding_fuel_weight(&self) -> Fuel {
+        self.weight.required_fuel()
+    }
+
+    fn fuel_including_fuel_weight(&self) -> Fuel {
+        iter::successors(Some(self.weight.required_fuel()), |fuel| {
+            if fuel.weight().is_zero() {
+                None
+            } else {
+                Some(fuel.weight().required_fuel())
+            }
+        })
+        .sum()
+    }
+}
+
+struct Weight(u32);
+
+impl Weight {
+    fn is_zero(&self) -> bool {
+        self.0 == 0
+    }
+
+    fn required_fuel(&self) -> Fuel {
+        Fuel((self.0 / 3).saturating_sub(2))
+    }
+}
+
+#[derive(Debug)]
+struct Fuel(u32);
+
+impl Fuel {
+    fn weight(&self) -> Weight {
+        Weight(self.0)
+    }
+}
+
+impl Add for Fuel {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        Fuel(self.0 + other.0)
+    }
+}
+
+impl Sum for Fuel {
+    fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
+        iter.fold(Fuel(0), Add::add)
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..0c24a73 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,12 @@
+use std::io;
+use std::io::prelude::*;
+
 fn main() {
-    println!("Hello, world!");
+    let stdin = io::stdin();
+    let answer = string_length_sum(stdin.lock().lines().map(|l| l.unwrap()));
+    dbg!(answer);
+}
+
+fn string_length_sum(it: impl Iterator<Item = String>) -> usize {
+    it.map(|l| l.len()).sum()
 }
-- 
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