Day seven

day-07-rust/src/task1.rs

@@ -0,0 +1,44 @@
+use crate::common;
+use crate::common::Number;
+use std::io::{BufReader, Read};
+use std::ops::Rem;
+
+pub(crate) fn run<R: Read>(read: R) {
+    let mut reader = BufReader::new(read).bytes().peekable();
+
+    let mut total = 0;
+    while let Some((result, parts)) = common::read_input_line(&mut reader) {
+        if let Some(ops) = brute(result, &parts) {
+            println!("{:?} & {:?} => {}", ops, parts, result);
+            total += result;
+        }
+    }
+
+    println!("Result: {}", total);
+}
+
+fn brute(result: Number, parts: &[Number]) -> Option<Vec<char>> {
+    match parts.split_last() {
+        None => None,
+        Some((last, [])) => {
+            if result == *last {
+                Some(vec![])
+            } else {
+                None
+            }
+        }
+        Some((cur, parts)) => {
+            let test_result = result - cur;
+            if let Some(mut ops) = brute(test_result, parts) {
+                ops.push('+');
+                return Some(ops);
+            }
+            let test_result = result / cur;
+            if result.rem(cur) == 0 && let Some(mut ops) = brute(test_result, parts) {
+                ops.push('*');
+                return Some(ops);
+            }
+            None
+        }
+    }
+}