diff --git a/src/engine.rs b/src/engine.rs
index 048514b..e936270 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -1,7 +1,7 @@
 use crate::config::Engine;
 
 pub trait InputEngine {
-   fn get(&self) -> String;
+   fn get(&self) -> Vec<char>;
 }
 
 pub fn build_input_engine(cfg: &Engine) -> Result<Box<dyn InputEngine>, String> {
@@ -14,11 +14,11 @@ pub fn build_input_engine(cfg: &Engine) -> Result<Box<dyn InputEngine>, String>
 struct InputEngineStdin {}
 
 impl InputEngine for InputEngineStdin {
-   fn get(&self) -> String {
+   fn get(&self) -> Vec<char> {
       let stdin = std::io::stdin();
       let mut result = String::new();
       stdin.read_line(&mut result).unwrap();
-      return result.trim().to_string();
+      return result.trim().chars().collect();
    }
 }
 
@@ -28,8 +28,8 @@ mod test_input {
 
    struct InputEngineTest {}
    impl InputEngine for InputEngineTest {
-      fn get(&self) -> String {
-         return "hello world".to_string();
+      fn get(&self) -> Vec<char> {
+         return "hello world".chars().collect();
       }
    }
 
@@ -40,12 +40,12 @@ mod test_input {
    }
 
    fn _test_input_engine_impl(engine: &dyn InputEngine) {
-      assert_eq!("hello world".to_string(), engine.get());
+      assert_eq!("hello world".to_string(), engine.get().iter().cloned().collect::<String>());
    }
 }
 
 pub trait OutputEngine {
-   fn put(&self, v: String);
+   fn put(&self, v: Vec<char>);
 }
 
 pub fn build_output_engine(cfg: &Engine) -> Result<Box<dyn OutputEngine>, String> {
@@ -58,8 +58,8 @@ pub fn build_output_engine(cfg: &Engine) -> Result<Box<dyn OutputEngine>, String
 struct OutputEngineStdout {}
 
 impl OutputEngine for OutputEngineStdout {
-   fn put(&self, v: String) {
-      println!("{}", v);
+   fn put(&self, v: Vec<char>) {
+      println!("{}", v.iter().cloned().collect::<String>());
    }
 }
 
@@ -69,7 +69,7 @@ mod test_output {
 
    struct OutputEngineTest {}
    impl OutputEngine for OutputEngineTest {
-      fn put(&self, _v: String) {
+      fn put(&self, _v: Vec<char>) {
       }
    }
 
@@ -80,6 +80,6 @@ mod test_output {
    }
 
    fn _test_output_engine_impl(engine: &dyn OutputEngine) {
-      engine.put("teehee".to_string());
+      engine.put("teehee".to_string().chars().collect());
    }
 }