diff --git a/arrays_and_strings/str-longest-non-repeating.py b/arrays_and_strings/str-longest-non-repeating.py
new file mode 100644
index 0000000..62c1008
--- /dev/null
+++ b/arrays_and_strings/str-longest-non-repeating.py
@@ -0,0 +1,38 @@
+### find the length of the longest substring without repeating characters
+
+
+def length_longest_substring(s: str) -> int:
+        
+        result = ""
+        this_longest_string = ""
+        
+        i = 0
+        
+        for c in s:
+            
+            j = 0
+        
+            # this loop breaks if repeated
+            while j < len(this_longest_string):
+                
+                if c == this_longest_string[j]:
+                    if len(this_longest_string) > len(result):
+                        result = this_longest_string
+                    this_longest_string = this_longest_string[j+1:]
+                    
+                j += 1
+            
+            # this loop continues creating the string
+            this_longest_string += c
+                
+            
+        return result, this_longest_string
+            
+                
+
+if __name__ == "__main__":
+    s = "abcabcbb"
+    print(length_longest_substring(s))
+
+    s = "dvdf"
+    print(length_longest_substring(s))