Add day02, 2019

3 files changed, 101 insertions, 0 deletions

diff --git a/2019/rust/Cargo.toml b/2019/rust/Cargo.toml
index f2bad2a..d52cdc3 100644
--- a/2019/rust/Cargo.toml
+++ b/2019/rust/Cargo.toml
@@ -1,4 +1,5 @@
 [workspace]
 members = [
     "day01",
+    "day02",
 ]
diff --git a/2019/rust/day02/Cargo.toml b/2019/rust/day02/Cargo.toml
new file mode 100644
index 0000000..bd205ba
--- /dev/null
+++ b/2019/rust/day02/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "day02"
+version = "0.1.0"
+authors = ["cos <cos>"]
+edition = "2018"
+
+[dependencies]
diff --git a/2019/rust/day02/src/main.rs b/2019/rust/day02/src/main.rs
new file mode 100644
index 0000000..0d3362a
--- /dev/null
+++ b/2019/rust/day02/src/main.rs
@@ -0,0 +1,93 @@
+use std::io::{self, BufRead};
+use std::env;
+
+// https://stackoverflow.com/q/37888042/remove-single-trailing-newline-from-string-without-cloning
+fn trim_newline(s: &mut String) {
+    if s.ends_with('\n') {
+        s.pop();
+        if s.ends_with('\r') {
+            s.pop();
+        }
+    }
+}
+
+fn read_input() -> Vec<usize> {
+    let stdin = io::stdin();
+
+    // Far from neat, but gets the job done...
+    stdin.lock().split(b',').map(|v| {
+        let mut s = String::from_utf8(v.unwrap()).unwrap();
+        trim_newline(&mut s);
+        let u:u32 = s.parse().unwrap();
+        u as usize
+    }).collect()
+}
+
+fn restore_gravity_assist(window:&mut [usize], noun:usize, verb:usize) {
+    window[0] = noun;
+    window[1] = verb;
+}
+
+fn add(ip:usize, memory:&mut Vec<usize>) {
+    let result = memory[ip + 3];
+    let left = memory[ip + 1];
+    let right = memory[ip + 2];
+    memory[result] = memory[left] + memory[right];
+}
+
+fn mul(ip:usize, memory:&mut Vec<usize>) {
+    let result = memory[ip + 3];
+    let left = memory[ip + 1];
+    let right = memory[ip + 2];
+    memory[result] = memory[left] * memory[right];
+}
+
+fn intcode(mut memory:Vec<usize>) -> usize {
+    let mut ip = 0;
+    while ip < memory.len() {
+        let op = memory[ip];
+        match op {
+            1 => { add(ip, &mut memory); ip += 4 },
+            2 => { mul(ip, &mut memory); ip += 4 },
+            99 => break,
+            op => panic!("Invalid operation {}", op),
+        }
+    }
+    memory[0]
+}
+
+fn first_puzzle(mut memory:Vec<usize>) -> usize {
+    println!("No argument provided, hence attemping to solve first puzzle.");
+
+    restore_gravity_assist(&mut memory[1..3], 12, 2);
+    intcode(memory)
+}
+
+fn second_puzzle(desired:usize, mut memory:Vec<usize>) -> Option<usize> {
+    println!("Desired output {} specified. Assuming second puzzle to search for it.", desired);
+    for noun in 0..100 {
+        for verb in 0..100 {
+            restore_gravity_assist(&mut memory[1..3], noun, verb);
+            if intcode(memory.clone()) == desired {
+                return Some(100 * noun + verb);
+            }
+        }
+    }
+
+    None
+}
+
+fn main() {
+    let memory = read_input();
+
+    let needle = env::args().nth(1);
+    let solution = match needle {
+        None    => Some(first_puzzle(memory)),
+        Some(n) => second_puzzle(n.parse().unwrap_or(0), memory),
+    };
+
+    match solution {
+        Some(s) => println!("Solution: {}.", s),
+        _       => println!("No solution found."),
+    }
+}