day 3

day-03/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day-03"
+version = "0.1.0"

day-03/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "day-03"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day-03/src/main.rs

@@ -0,0 +1,70 @@
+const INPUT: &str = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/input.txt"));
+
+fn main() {
+    let mut idx = 0;
+    let mut total = 0;
+    while idx < INPUT.len() {
+        if let Some((num, temp)) = parse_mul(INPUT, idx) {
+            total += num;
+            idx = temp;
+        } else {
+            idx += 1;
+        }
+    }
+
+    println!("Part 1: {}", total);
+
+    let mut idx = 0;
+    let mut conditional = 0;
+    let mut permitted = true;
+    while idx < INPUT.len() {
+        if let Some(temp) = parse_lit(INPUT, idx, "do()") {
+            idx = temp;
+            permitted = true;
+        } else if let Some(temp) = parse_lit(INPUT, idx, "don't()") {
+            idx = temp;
+            permitted = false;
+        }
+        else if let Some((num, temp)) = parse_mul(INPUT, idx) {
+            idx = temp;
+
+            if permitted {
+                conditional += num;
+            }
+        } else {
+            idx += 1;
+        }
+    }
+
+    println!("Part 2: {}", conditional);
+}
+
+fn parse_num(src: &str, mut idx: usize) -> Option<(u32, usize)> {
+    let start = idx;
+    let mut chars = src[idx..].chars();
+    while chars.next().is_some_and(|c| c.is_numeric()) {
+        idx += 1;
+    }
+
+    if idx != start {
+        Some((str::parse::<u32>(&src[start..idx]).unwrap(), idx))
+    } else { None }
+}
+
+fn parse_lit(src: &str, idx: usize, exp: &str) -> Option<usize> {
+    if src[idx..].starts_with(exp) {
+        Some(idx + exp.len())
+    } else {
+        None
+    }
+}
+
+fn parse_mul(src: &str, mut idx: usize) -> Option<(u32, usize)> {
+    idx = parse_lit(src, idx, "mul(")?;
+    let (first, mut idx) = parse_num(src, idx)?;
+    idx = parse_lit(src, idx, ",")?;
+    let (second, mut idx) = parse_num(src, idx)?;
+    idx = parse_lit(src, idx, ")")?;
+
+    Some((first * second, idx))
+}