diff --git a/src/robot.rs b/src/robot.rs
index 59fa0bd..09901c4 100644
--- a/src/robot.rs
+++ b/src/robot.rs
@@ -9,11 +9,15 @@ pub struct Robot {
 
 impl Robot {
     /// Create new `Robot` with given id, `Orientation`, `Position` and instructions.
-    fn new(id: i32, o: Orientation, p: Position, i: Vec<char>) -> Robot {
+    fn new(id: u32, o: Orientation, p: Position, i: Vec<char>) -> Robot {
         Robot { id, o, p, i }
     }
     /// Apply given instruction to a `Robot`.
-    fn execute_instruction(&mut self) -> Result<(), &'static str> {
+    fn execute_instruction(
+        &mut self,
+        hash: &mut std::collections::HashMap<Position, u32>,
+    ) -> Result<(), &'static str> {
+        hash.remove(&self.p); // we need to insert the new position after calling execute_instruction()
         match self.i.pop() {
             Some(instruction) => match instruction {
                 'L' => Ok(match self.o {
@@ -50,6 +54,7 @@ enum Orientation {
 }
 
 /// Struct to store robot position.
+#[derive(PartialEq, Eq, Hash)]
 struct Position {
     x: i32,
     y: i32,