add: day 7

.editorconfig

@@ -15,3 +15,7 @@ trim_trailing_whitespace = false
 
 [*.md]
 trim_trailing_whitespace = false
+
+[Makefile]
+indent_style = tab
+tab_width = 4

Makefile

@@ -0,0 +1,5 @@
+aoc_test:
+	cargo test --bin 07 -- --nocapture
+
+solve:
+	cargo solve 6

data/examples/07.txt

@@ -0,0 +1,9 @@
+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

src/bin/07.rs

@@ -0,0 +1,105 @@
+advent_of_code::solution!(7);
+
+pub fn part_one(input: &str) -> Option<u64> {
+    let mut ans = 0;
+
+    let equations = parse_input(input);
+    for eq in equations {
+        if bt(eq.nums[0], &eq.answer, &eq.nums, 1) {
+            ans += eq.answer;
+        }
+    }
+
+    Some(ans)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let mut ans = 0;
+
+    let equations = parse_input(input);
+    for eq in equations {
+        if bt2(eq.nums[0], &eq.answer, &eq.nums, 1) {
+            ans += eq.answer;
+        }
+    }
+
+    Some(ans)
+}
+
+#[derive(Debug)]
+struct Equation {
+    answer: u64,
+    nums: Vec<u64>,
+}
+
+fn parse_input(input: &str) -> Vec<Equation> {
+    let mut equations = vec![];
+    for line in input.lines() {
+        let (answer, nums) = line.split_once(':').unwrap();
+        let eq = Equation {
+            answer: answer.parse::<u64>().unwrap(),
+            nums: nums
+                .split_whitespace()
+                .map(|num| num.parse::<u64>().unwrap())
+                .collect(),
+        };
+        equations.push(eq);
+    }
+    equations
+}
+
+fn bt(curr_val: u64, answer: &u64, nums: &Vec<u64>, i: usize) -> bool {
+    if curr_val > *answer {
+        return false;
+    }
+    if i == nums.len() {
+        return curr_val == *answer;
+    }
+
+    let next_val = nums[i];
+
+    bt(curr_val * next_val, answer, nums, i + 1) || bt(curr_val + next_val, answer, nums, i + 1)
+}
+
+fn bt2(curr_val: u64, answer: &u64, nums: &Vec<u64>, i: usize) -> bool {
+    if curr_val > *answer {
+        return false;
+    }
+    if i == nums.len() {
+        return curr_val == *answer;
+    }
+
+    let next_val = nums[i];
+
+    if let Some(concat_val) = concat_nums(curr_val, &next_val) {
+        if bt2(concat_val, answer, nums, i + 1) {
+            return true;
+        }
+    }
+
+    bt2(curr_val * next_val, answer, nums, i + 1) || bt2(curr_val + next_val, answer, nums, i + 1)
+}
+
+fn concat_nums(num1: u64, num2: &u64) -> Option<u64> {
+    let new_num = num1.to_string() + &num2.to_string();
+    let new_num = new_num.parse::<u64>().ok()?;
+
+    Some(new_num)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let result = part_one(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(3749));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let result = part_two(&advent_of_code::template::read_file("examples", DAY));
+        assert_eq!(result, Some(11387));
+    }
+}