diff --git a/src/playfield.rs b/src/playfield.rs
index 1bd2d49..952786c 100644
--- a/src/playfield.rs
+++ b/src/playfield.rs
@@ -1,9 +1,10 @@
 use std::fmt;
+
 #[derive(PartialEq, Debug, Clone)]
 pub struct Playfield {
     size: usize,
     pub fields: Vec<Vec<Field>>,
-    open_fields: Vec<u32>,
+    pub open_fields: Vec<usize>,
 }
 
 impl Playfield {
@@ -11,7 +12,7 @@ impl Playfield {
         Self {
             size,
             fields: vec![vec![Field::default(); size]; size],
-            open_fields: Vec::<u32>::new(),
+            open_fields: Vec::new(),
         }
     }
     pub fn new(field: &String, size: usize) -> Playfield {
@@ -34,10 +35,12 @@ impl Playfield {
 
         for row in 0..self.size {
             for col in 0..self.size {
+                let index = row * self.size + col;
                 let field = &mut self.fields[row][col];
-                let char_field = chars.get(row * self.size + col).unwrap();
+                let char_field = chars.get(index).unwrap();
 
                 if *char_field == "0" {
+                    self.open_fields.push(index);
                     continue;
                 }
 
@@ -75,7 +78,7 @@ pub struct Field {
 impl Field {
     fn default() -> Field {
         Self {
-            possible_values: Vec::<u32>::new(),
+            possible_values: Vec::new(),
             value: None,
         }
     }
@@ -88,7 +91,7 @@ mod tests {
     impl Field {
         fn new(value: u32) -> Field {
             Self {
-                possible_values: Vec::<u32>::new(),
+                possible_values: Vec::new(),
                 value: Some(value),
             }
         }
diff --git a/src/sudoku_solver b/src/sudoku_solver
deleted file mode 100644
index 532d99d..0000000
--- a/src/sudoku_solver
+++ /dev/null
@@ -1,7 +0,0 @@
-struct SudokuSolver {
-  playfield: Playfield
-}
-
-impl SudokuSolver {
-
-}
diff --git a/src/sudoku_solver.rs b/src/sudoku_solver.rs
index 7cc8606..a2ba2ed 100644
--- a/src/sudoku_solver.rs
+++ b/src/sudoku_solver.rs
@@ -1,10 +1,11 @@
+use crate::playfield::Field;
 use crate::playfield::Playfield;
 
 pub struct SudokuSolver {
     playfield: Playfield,
 }
 
-impl SudokuSolver {
+impl<'a> SudokuSolver {
     pub fn new(playfield: &Playfield) -> SudokuSolver {
         Self {
             playfield: playfield.clone(),
@@ -15,27 +16,41 @@ impl SudokuSolver {
     }
 
     fn populate_possible_values(&self) {
-        for row in &self.playfield.fields {
-            for field in row {
-                if field.value.is_some() {
-                    continue;
-                }
-            }
-        }
+        for open_field in &self.playfield.open_fields {}
     }
+    fn possible_values_from_row(&self, row: Vec<Field>) -> Vec<u32> {}
 }
 #[cfg(test)]
 mod tests {
+    use crate::sudoku_solver::SudokuSolver;
+    use crate::Playfield;
+    fn create_test_playfield(input: &str, size: usize) -> Playfield {
+        Playfield::new(&input.to_string(), size)
+    }
     mod solve {
-        use super::super::*;
+        use super::*;
         #[test]
         fn simple() {
-            let playfield = Playfield::new(&"1 2 3 2 3 1 3 1 0".to_string(), 3);
-            let expected = Playfield::new(&"1 2 3 2 3 1 3 1 2".to_string(), 3);
+            let playfield = create_test_playfield("1 2 3 2 3 1 3 1 0", 3);
+            let expected = create_test_playfield("1 2 3 2 3 1 3 1 2", 3);
 
             let solved = SudokuSolver::new(&playfield).solve();
 
             assert_eq!(solved, expected);
         }
     }
+    mod populate_possible_values {
+        mod possible_values_from_row {
+            use super::super::*;
+            #[test]
+            fn simple() {
+                let playfield = create_test_playfield("1 2 0 1 2 0 1 2 0", 3);
+                let expected = vec![3];
+
+                let possible_values =
+                    SudokuSolver::new(&playfield).possible_values_from_row(playfield.fields[0]);
+                assert_eq!(possible_values, expected);
+            }
+        }
+    }
 }