day 7

day-07/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "day-07"
+version = "0.1.0"

day-07/Cargo.toml

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+[package]
+name = "day-07"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

day-07/src/main.rs

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+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
+    }
+}
+

day-07/src/out.txt

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+Part 1: 456565678667482