From 756c29ad71e08143a4415ab233a5056237f7825e Mon Sep 17 00:00:00 2001
From: Wesley Moore <wes@wezm.net>
Date: Mon, 2 Dec 2019 21:25:53 +1100
Subject: [PATCH] Day 2 part 1

---
 2019/input/day2.txt  |  1 +
 2019/src/bin/day2.rs | 63 ++++++++++++++++++++++++++++++++++++++++++++
 2019/src/input.rs    | 11 ++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 2019/input/day2.txt
 create mode 100644 2019/src/bin/day2.rs

diff --git a/2019/input/day2.txt b/2019/input/day2.txt
new file mode 100644
index 0000000..32f1f63
--- /dev/null
+++ b/2019/input/day2.txt
@@ -0,0 +1 @@
+1,0,0,3,1,1,2,3,1,3,4,3,1,5,0,3,2,10,1,19,1,19,9,23,1,23,6,27,1,9,27,31,1,31,10,35,2,13,35,39,1,39,10,43,1,43,9,47,1,47,13,51,1,51,13,55,2,55,6,59,1,59,5,63,2,10,63,67,1,67,9,71,1,71,13,75,1,6,75,79,1,10,79,83,2,9,83,87,1,87,5,91,2,91,9,95,1,6,95,99,1,99,5,103,2,103,10,107,1,107,6,111,2,9,111,115,2,9,115,119,2,13,119,123,1,123,9,127,1,5,127,131,1,131,2,135,1,135,6,0,99,2,0,14,0
diff --git a/2019/src/bin/day2.rs b/2019/src/bin/day2.rs
new file mode 100644
index 0000000..5b88abb
--- /dev/null
+++ b/2019/src/bin/day2.rs
@@ -0,0 +1,63 @@
+use std::{fs, io};
+
+use advent_of_code::input;
+
+fn main() -> io::Result<()> {
+    let input = fs::read_to_string("input/day2.txt")?;
+    let mut program = input::read_separated_line(',', &input)?;
+
+    // To do this, before running the program, replace position 1 with the value 12 and replace
+    // position 2 with the value 2. What value is left at position 0 after the program halts?
+    program[1] = 12;
+    program[2] = 2;
+    run_program(&mut program);
+
+    println!("Part 1: {}", program[0]);
+
+    Ok(())
+}
+
+fn run_program(program: &mut [i32]) {
+    let mut addr = 0;
+
+    loop {
+        match program[addr] {
+            1 => {
+                program[program[addr + 3] as usize] =
+                    program[program[addr + 1] as usize] + program[program[addr + 2] as usize]
+            }
+            2 => {
+                program[program[addr + 3] as usize] =
+                    program[program[addr + 1] as usize] * program[program[addr + 2] as usize]
+            }
+            99 => break,
+            opcode => panic!("Invalid opcode {}", opcode),
+        }
+
+        addr += 4;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example1() {
+        let input = "1,0,0,0,99";
+        let mut program = input::read_separated_line(',', &input).unwrap();
+
+        run_program(&mut program);
+
+        assert_eq!(program, &[2, 0, 0, 0, 99])
+    }
+    #[test]
+    fn test_example4() {
+        let input = "1,1,1,4,99,5,6,0,99";
+        let mut program = input::read_separated_line(',', &input).unwrap();
+
+        run_program(&mut program);
+
+        assert_eq!(program, &[30, 1, 1, 4, 2, 5, 6, 0, 99])
+    }
+}
diff --git a/2019/src/input.rs b/2019/src/input.rs
index 31a06e6..f59098b 100644
--- a/2019/src/input.rs
+++ b/2019/src/input.rs
@@ -17,3 +17,14 @@ pub fn read_number_list<P: AsRef<Path>>(path: P) -> io::Result<Vec<i32>> {
 
     Ok(output)
 }
+
+pub fn read_separated_line(sep: char, line: &str) -> io::Result<Vec<i32>> {
+    line.trim()
+        .split(sep)
+        .map(|number| {
+            number
+                .parse()
+                .map_err(|err| io::Error::new(io::ErrorKind::InvalidInput, err))
+        })
+        .collect()
+}