From d7fbfa44e1f7b1b21b0800870576ea75d07439a1 Mon Sep 17 00:00:00 2001
From: Aaron Manning <contact@aaronmanning.net>
Date: Sat, 7 Dec 2024 18:38:11 +1100
Subject: [PATCH] day 7

---
 day-07/Cargo.lock  |  7 +++++
 day-07/Cargo.toml  |  6 ++++
 day-07/src/main.rs | 78 ++++++++++++++++++++++++++++++++++++++++++++++
 day-07/src/out.txt |  1 +
 4 files changed, 92 insertions(+)
 create mode 100644 day-07/Cargo.lock
 create mode 100644 day-07/Cargo.toml
 create mode 100644 day-07/src/main.rs
 create mode 100644 day-07/src/out.txt

diff --git a/day-07/Cargo.lock b/day-07/Cargo.lock
new file mode 100644
index 0000000..fe8fa1a
--- /dev/null
+++ b/day-07/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day-07"
+version = "0.1.0"
diff --git a/day-07/Cargo.toml b/day-07/Cargo.toml
new file mode 100644
index 0000000..daf428a
--- /dev/null
+++ b/day-07/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day-07"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/day-07/src/main.rs b/day-07/src/main.rs
new file mode 100644
index 0000000..a445210
--- /dev/null
+++ b/day-07/src/main.rs
@@ -0,0 +1,78 @@
+const INPUT: &str = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/input.txt"));
+
+fn main() {
+
+    let eqns = INPUT.lines().map(|line| {
+        let (test, operands) = line.split_once(':').unwrap();
+        let test = test.parse::<u64>().unwrap();
+        let operands = operands
+            .trim_start_matches(':')
+            .split_whitespace()
+            .map(|num| num.parse::<u64>().unwrap())
+            .collect::<Vec<_>>();
+        (test, operands)
+    });
+
+    {
+        let mut total = 0;
+
+        for (test, operands) in eqns.clone() {
+            if let Some((start, rest)) = operands.split_first() {
+                total += u64::from(check_matches(*start, test, rest, false)) * test;
+            }
+        }
+        println!("Part 1: {}", total);
+    }
+
+    {
+        let mut total = 0;
+
+        for (test, operands) in eqns {
+            if let Some((start, rest)) = operands.split_first() {
+                total += u64::from(check_matches(*start, test, rest, true)) * test;
+            }
+        }
+        println!("Part 2: {}", total);
+    }
+}
+
+
+fn check_matches(curr: u64, test: u64, operands: &[u64], include_concat: bool) -> bool {
+    match operands.split_first() {
+        Some((first, rest)) => {
+               check_matches(curr + first, test, rest, include_concat)
+            || check_matches(curr * first, test, rest, include_concat)
+            || (include_concat && check_matches(concat(curr, *first), test, rest, include_concat))
+        }
+        None => {
+            curr == test
+        }
+    }
+}
+
+fn concat(left: u64, right: u64) -> u64 {
+    left * 10u64.pow(digits(right)) + right
+}
+
+pub (crate) fn digits(mut number: u64) -> u32 {
+    if number < 100 {
+        if number < 10 {
+            1
+        } else {
+            2
+        }
+    } else if number < 1000 {
+        3
+    } else if number < 10000 {
+        4
+    } else {
+        number /= 10000;
+        let mut digits = 4;
+        while number != 0 {
+            number /= 10;
+            digits += 1;
+        }
+        digits
+    }
+}
+
diff --git a/day-07/src/out.txt b/day-07/src/out.txt
new file mode 100644
index 0000000..35b81c3
--- /dev/null
+++ b/day-07/src/out.txt
@@ -0,0 +1 @@
+Part 1: 456565678667482