diff --git a/solutions/modify_letter/src/lib.rs b/solutions/modify_letter/src/lib.rs
index 556d514c..5a3be843 100644
--- a/solutions/modify_letter/src/lib.rs
+++ b/solutions/modify_letter/src/lib.rs
@@ -3,28 +3,17 @@ pub fn remove_letter_sensitive(s: &str, letter: char) -> String {
 }
 
 pub fn remove_letter_insensitive(s: &str, letter: char) -> String {
-    let lower_letter = letter.to_lowercase().to_string();
-    let upper_letter = letter.to_uppercase().to_string();
-    s.replace(&upper_letter, &lower_letter)
-        .replace(&lower_letter, "")
+    s.chars().filter(|&c| c.to_ascii_lowercase() != letter.to_ascii_lowercase()).collect()
 }
 
 pub fn swap_letter_case(s: &str, letter: char) -> String {
-    s.split("")
-        .into_iter()
-        .map(|s| {
-            s.chars()
-                .filter_map(|c| {
-                    if c.to_string() == letter.to_lowercase().to_string() {
-                        c.to_uppercase().next()
-                    } else if c.to_string() == letter.to_uppercase().to_string() {
-                        c.to_lowercase().next()
-                    } else {
-                        Some(c)
-                    }
-                })
-                .collect()
-        })
-        .collect::<Vec<String>>()
-        .join("")
+   s.chars()
+        .map(|c| (
+            if c.to_ascii_lowercase() == letter.to_ascii_lowercase() {
+                if c.is_ascii_lowercase() { c.to_ascii_uppercase() } else { c.to_ascii_lowercase() }
+            } else {
+                c
+            }
+        ))
+        .collect()
 }