Better permutation creation

day_07/src/equation.rs

@@ -1,7 +1,11 @@
 mod operator_set;
 
+use std::collections::HashSet;
+
 use operator_set::{Op, create_operator_set};
 
+use crate::equation::operator_set::create_permutations;
+
 #[derive(Debug)]
 pub struct Equation {
     answer: i64,
@@ -63,8 +67,11 @@ impl Equation {
         accumulator
     }
 
-    pub fn solvable(&self) -> bool {
+    pub fn solvable_multiply_add(&self) -> bool {
-        let op_combinations = create_operator_set(self.components.len() - 1);
+        let op_combinations = create_permutations(
+            HashSet::from([Op::Add, Op::Multiply]),
+            self.components.len() - 1,
+        );
 
         for combination in op_combinations {
             if self.answer == self.compute_answer(&combination) {

day_07/src/equation/operator_set.rs

@@ -57,3 +57,27 @@ pub fn create_operator_set(num_of_operators: usize) -> HashSet<Vec<Op>> {
 
     operator_sets
 }
+
+fn create_permutations_recurse(
+    values: &HashSet<Op>,
+    len: usize,
+    permutations: &mut HashSet<Vec<Op>>,
+    curr_permutation: Vec<Op>,
+) {
+    if curr_permutation.len() == len {
+        permutations.insert(curr_permutation);
+        return;
+    }
+
+    for v in values {
+        let mut next_permutation = curr_permutation.clone();
+        next_permutation.push(*v);
+        create_permutations_recurse(values, len, permutations, next_permutation);
+    }
+}
+
+pub fn create_permutations(set: HashSet<Op>, len: usize) -> HashSet<Vec<Op>> {
+    let mut permutations = HashSet::new();
+    create_permutations_recurse(&set, len, &mut permutations, vec![]);
+    permutations
+}

day_07/src/main.rs

@@ -38,7 +38,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     println!("Is solvable?");
     println!("------------");
     for equation in equations {
-        let solvable = equation.solvable();
+        let solvable = equation.solvable_multiply_add();
         println!("{:?} => {}", equation, solvable);
         if solvable {
             value_sum += equation.answer();