day 7 part 2

src/day07.rs

@@ -22,15 +22,15 @@ fn part1(input: &str) -> RiddleResult {
                 .map(|capture| capture.as_str().parse::<i64>().unwrap())
                 .collect_vec()
         })
-        .filter(well_calibrated)
+        .filter(|v| well_calibrated(v, false))
         .map(|v| v[0])
         .sum()
 }
 
-fn well_calibrated(list: &Vec<i64>) -> bool {
+fn well_calibrated(list: &Vec<i64>, concat: bool) -> bool {
     let expected = list[0];
     let operands = list.iter().skip(1).copied().collect_vec();
-    let operators = ops(operands.len() - 1);
+    let operators = ops(operands.len() - 1, concat);
     for ops in operators.into_iter() {
         // dbg!(&ops);
         let v = ops
@@ -39,6 +39,7 @@ fn well_calibrated(list: &Vec<i64>) -> bool {
             .fold(operands[0], |acc, (op, val)| match op {
                 '*' => acc * val,
                 '+' => acc + val,
+                '|' => format!("{acc}{val}").parse().unwrap(),
                 _ => panic!(),
             });
         if v == expected {
@@ -48,24 +49,80 @@ fn well_calibrated(list: &Vec<i64>) -> bool {
     false
 }
 
-fn ops(n: usize) -> Vec<Vec<char>> {
+fn ops(n: usize, concat: bool) -> Vec<Vec<char>> {
     if n == 1 {
-        return vec![vec!['+'], vec!['*']];
+        let mut v = vec![vec!['+'], vec!['*']];
+        if concat {
+            v.push(vec!['|']);
+        }
+        return v;
     }
-    let v = ops(n - 1);
+    let v = ops(n - 1, concat);
     v.into_iter()
         .flat_map(|vector| {
-            let mut v1 = vector.clone();
-            let mut v2 = vector;
-            v1.push('+');
-            v2.push('*');
-            [v1, v2]
+            if !concat {
+                let mut v1 = vector.clone();
+                let mut v2 = vector;
+                v1.push('+');
+                v2.push('*');
+
+                vec![v1, v2]
+            } else {
+                let mut v1 = vector.clone();
+                let mut v2 = vector.clone();
+                let mut v3 = vector.clone();
+                let mut v4 = vector.clone();
+                let mut v5 = vector.clone();
+                let mut v6 = vector.clone();
+                let mut v7 = vector.clone();
+                let mut v8 = vector.clone();
+                let mut v9 = vector;
+                v1.push('+');
+                v2.push('+');
+                v3.push('+');
+                v4.push('*');
+                v5.push('*');
+                v6.push('*');
+                v7.push('|');
+                v8.push('|');
+                v9.push('|');
+
+                vec![v1, v2, v3, v4, v5, v6, v7, v8, v9]
+            }
         })
         .collect_vec()
 }
 
-fn part2(_input: &str) -> RiddleResult {
-    0
+fn part2(input: &str) -> RiddleResult {
+    let regex = Regex::new("(\\d+)").unwrap();
+    input
+        .lines()
+        .map(|line| {
+            regex
+                .find_iter(line)
+                .map(|capture| capture.as_str().parse::<i64>().unwrap())
+                .collect_vec()
+        })
+        .filter(|v| well(v[0], v[1], &v[2..]))
+        .map(|v| v[0])
+        .sum()
+}
+
+fn well(expected: i64, acc: i64, operands: &[i64]) -> bool {
+    if operands.is_empty() {
+        return expected == acc;
+    }
+
+    let next = operands[0];
+    let remainder = &operands[1..];
+
+    let v_mul = acc * next;
+    let v_plus = acc + next;
+    let v_concat = format!("{acc}{next}").parse().unwrap();
+    well(expected, v_mul, remainder)
+        || well(expected, v_plus, remainder)
+        || well(expected, v_concat, remainder)
+    // _ => panic!(),
 }
 
 #[cfg(test)]
@@ -89,6 +146,6 @@ mod test {
 
     #[test]
     fn test2() {
-        assert_eq!(part2(TEST_INPUT), 0);
+        assert_eq!(part2(TEST_INPUT), 11387);
     }
 }