From e8a0fa1627d1ebfae0083a86a589d71d5326ddc9 Mon Sep 17 00:00:00 2001
From: "Eric N. Vander Weele" <ericvw@gmail.com>
Date: Sun, 28 Jan 2024 17:37:29 -0500
Subject: [PATCH] 2019: Day 2

---
 2019/input_02.txt         |  1 +
 2019/src/bin/puzzle_02.rs | 77 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)
 create mode 100644 2019/input_02.txt
 create mode 100644 2019/src/bin/puzzle_02.rs

diff --git a/2019/input_02.txt b/2019/input_02.txt
new file mode 100644
index 0000000..6ffe0d5
--- /dev/null
+++ b/2019/input_02.txt
@@ -0,0 +1 @@
+1,0,0,3,1,1,2,3,1,3,4,3,1,5,0,3,2,1,10,19,1,19,5,23,2,23,6,27,1,27,5,31,2,6,31,35,1,5,35,39,2,39,9,43,1,43,5,47,1,10,47,51,1,51,6,55,1,55,10,59,1,59,6,63,2,13,63,67,1,9,67,71,2,6,71,75,1,5,75,79,1,9,79,83,2,6,83,87,1,5,87,91,2,6,91,95,2,95,9,99,1,99,6,103,1,103,13,107,2,13,107,111,2,111,10,115,1,115,6,119,1,6,119,123,2,6,123,127,1,127,5,131,2,131,6,135,1,135,2,139,1,139,9,0,99,2,14,0,0
diff --git a/2019/src/bin/puzzle_02.rs b/2019/src/bin/puzzle_02.rs
new file mode 100644
index 0000000..2816b10
--- /dev/null
+++ b/2019/src/bin/puzzle_02.rs
@@ -0,0 +1,77 @@
+use std::convert::From;
+use std::io;
+use std::ops;
+
+enum Opcode {
+    Add = 1,
+    Multiply = 2,
+    Halt = 99,
+}
+
+impl From<u32> for Opcode {
+    fn from(x: u32) -> Self {
+        match x {
+            1 => Opcode::Add,
+            2 => Opcode::Multiply,
+            99 => Opcode::Halt,
+            _ => unreachable!(),
+        }
+    }
+}
+
+const INSTRUCTION_LEN: usize = 4;
+
+fn extract_parameters(instruction: &[u32]) -> (usize, usize, usize) {
+    (
+        usize::try_from(instruction[1]).unwrap(),
+        usize::try_from(instruction[2]).unwrap(),
+        usize::try_from(instruction[3]).unwrap(),
+    )
+}
+
+fn run_program(prog: &[u32], addr1_val: u32, addr2_val: u32) -> Vec<u32> {
+    let mut prog = prog.to_vec();
+
+    prog[1] = addr1_val;
+    prog[2] = addr2_val;
+
+    let mut idx: usize = 0;
+    loop {
+        match Opcode::from(prog[idx]) {
+            Opcode::Add => {
+                let (addr1, addr2, dst) = extract_parameters(&prog[idx..]);
+                prog[dst] = prog[addr1] + prog[addr2];
+            }
+            Opcode::Multiply => {
+                let (addr1, addr2, dst) = extract_parameters(&prog[idx..]);
+                prog[dst] = prog[addr1] * prog[addr2];
+            }
+            Opcode::Halt => break,
+        }
+
+        idx += INSTRUCTION_LEN;
+    }
+
+    prog
+}
+
+fn main() {
+    let intcode_prog: Vec<u32> = io::read_to_string(io::stdin())
+        .unwrap()
+        .trim()
+        .split(',')
+        .map(|x| x.parse().unwrap())
+        .collect();
+
+    println!("Part 1: {}", run_program(&intcode_prog, 12, 2)[0]);
+
+    const TARGET_OUTPUT: u32 = 19690720;
+    const INPUT_RANGE: ops::RangeInclusive<u32> = 0..=99;
+
+    let (noun, verb) = INPUT_RANGE
+        .flat_map(|noun| INPUT_RANGE.map(move |verb| (noun, verb)))
+        .find(|&(noun, verb)| run_program(&intcode_prog, noun, verb)[0] == TARGET_OUTPUT)
+        .unwrap();
+
+    println!("Part 2: {}", 100 * noun + verb);
+}