1 files changed, 50 insertions, 0 deletions
diff --git a/src/bin/day7.rs b/src/bin/day7.rs
new file mode 100644
index 0000000..60b08b1
--- /dev/null
+++ b/src/bin/day7.rs
@@ -0,0 +1,50 @@
+static DAY: u8 = 7;
+
+fn main() {
+    let input = advent::read_lines(DAY);
+    println!("{DAY}a: {}", calibration_result(&input));
+    println!("{DAY}b: {}", 0);
+}
+
+fn calculateable(result: i64, operands: &[i64]) -> bool {
+    if operands.len() == 1 {
+        return result == operands[0];
+    }
+    let rem = &operands[..=operands.len()-2];
+    let op = operands[operands.len()-1];
+    calculateable(result - op, rem) || (result % op == 0 && calculateable(result / op, rem))
+}
+
+fn calibration_result(input: &[String]) -> i64 {
+    let mut sum = 0;
+    for line in input {
+        let (result, operands) = line.split_once(": ").unwrap();
+        let result = result.parse::<i64>().unwrap();
+        let operands = operands.split(" ").map(|x| x.parse::<i64>().unwrap()).collect::<Vec<_>>();
+        if calculateable(result, &operands) {
+            sum += result;
+        }
+    }
+    sum
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "190: 10 19",
+            "3267: 81 40 27",
+            "83: 17 5",
+            "156: 15 6",
+            "7290: 6 8 6 15",
+            "161011: 16 10 13",
+            "192: 17 8 14",
+            "21037: 9 7 18 13",
+            "292: 11 6 16 20",
+        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
+        assert_eq!(calibration_result(&input), 3749);
+    }
+}