Implement remove_duplicate_chars function

solution2.py

@@ -1,2 +1,9 @@
 def remove_duplicate_chars(s: str) -> str:
-    pass
+    result = ""
+    for char in s:
+        if char not in result:
+            result += char
+    return result
+
+if __name__ == "__main__":
+    print(f"remove_duplicate_chars('abacabad') → {remove_duplicate_chars('abacabad')}")