diff --git a/src/days/d07.rs b/src/days/d07.rs
index f8e20e3..531bd25 100644
--- a/src/days/d07.rs
+++ b/src/days/d07.rs
@@ -2,31 +2,156 @@ use super::{Answer, Day, DayImpl};
 
 const CURRENT_DAY: u8 = 7;
 
-type Data = Vec<u64>;
+#[derive(Debug, Clone, Copy)]
+enum Operator {
+    Add,
+    Multiply,
+}
+
+impl Operator {
+    fn calculate(&self, a: u64, b: u64) -> u64 {
+        match self {
+            Operator::Multiply => a * b,
+            Operator::Add => a + b,
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct CombinationIterator<'a, T>
+where
+    T: Sized + Clone,
+{
+    iteration: usize,
+    length: u32,
+    possibilities: &'a [T],
+}
+
+impl<'a, T> CombinationIterator<'a, T>
+where
+    T: Sized + Clone,
+{
+    fn get_index_on_position(&self, position: u32) -> usize {
+        (if position == 0 {
+            self.iteration
+        } else {
+            self.iteration / (self.possibilities.len().pow(position))
+        }) % self.possibilities.len()
+    }
+
+    fn new(possibilities: &'a [T], length: u32) -> Self {
+        Self {
+            iteration: 0,
+            length,
+            possibilities,
+        }
+    }
+}
+
+impl<'a, T> Iterator for CombinationIterator<'a, T>
+where
+    T: Sized + Clone,
+{
+    type Item = Vec<T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.get_index_on_position(self.length) != 0 {
+            return None;
+        }
+
+        let values = (0..self.length)
+            .map(|p| self.possibilities[self.get_index_on_position(p)].clone())
+            .collect();
+        self.iteration += 1;
+        return Some(values);
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct CalibrationEquation {
+    pub result: u64,
+    pub parts: Vec<u64>,
+}
+
+impl CalibrationEquation {
+    fn calculate(&self, operations: Vec<Operator>) -> u64 {
+        let mut value = self.parts[0];
+
+        for i in 1..(self.parts.len()) {
+            value = operations[i - 1].calculate(value, self.parts[i]);
+        }
+
+        value
+    }
+
+    fn can_be_valid(&self) -> bool {
+        CombinationIterator::new(
+            &[Operator::Add, Operator::Multiply],
+            (self.parts.len() - 1) as u32,
+        )
+        .map(|o| self.calculate(o))
+        .collect::<Vec<_>>()
+        .contains(&self.result)
+    }
+}
+
+impl From<&str> for CalibrationEquation {
+    fn from(value: &str) -> Self {
+        let (first, second) = value.split_once(':').unwrap();
+
+        Self {
+            result: first.parse().unwrap(),
+            parts: second
+                .trim()
+                .split_whitespace()
+                .map(|v| v.parse().unwrap())
+                .collect(),
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Calibrator {
+    equations: Vec<CalibrationEquation>,
+}
+
+impl Calibrator {
+    pub fn get_valid_sum(&self) -> u64 {
+        self.equations
+            .iter()
+            .filter(|v| v.can_be_valid())
+            .map(|v| v.result)
+            .sum()
+    }
+}
+
+impl From<&str> for Calibrator {
+    fn from(value: &str) -> Self {
+        Self {
+            equations: value.lines().map(|v| v.into()).collect(),
+        }
+    }
+}
+
+type Data = Calibrator;
 impl DayImpl<Data> for Day<CURRENT_DAY> {
     fn init_test() -> (Self, Data) {
         Self::init(include_str!("test_inputs/test07.txt"))
     }
 
     fn expected_results() -> (Answer, Answer) {
-        (Answer::Number(0), Answer::Number(0))
+        (Answer::Number(3749), Answer::Number(0))
     }
 
     fn init(input: &str) -> (Self, Data) {
-        (
-            Self {},
-            input
-                .lines()
-                .map(|v| v.parse::<u64>().expect("error while parsing input."))
-                .collect(),
-        )
+        (Self {}, input.into())
     }
 
     fn one(&self, data: &mut Data) -> Answer {
-        Answer::Number(data.len() as u64)
+        Answer::Number(data.get_valid_sum())
     }
 
     fn two(&self, data: &mut Data) -> Answer {
-        Answer::Number(data.len() as u64)
+        Answer::Number(0)
     }
 }
diff --git a/src/days/test_inputs/test07.txt b/src/days/test_inputs/test07.txt
index e69de29..fc6e099 100644
--- a/src/days/test_inputs/test07.txt
+++ b/src/days/test_inputs/test07.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