Added task 3

basic programming/3rd task/6.py

@@ -0,0 +1,24 @@
+def duplicates_has(txt: str) -> str:
+    seen = ""
+    for char in txt:
+        if char in seen:
+            return char
+        seen += char
+    return None
+
+def main_6ex():
+    txt1 = "banana"
+    result = duplicates_has(txt1)
+    if result:
+        print(f'In {txt1} {result} appears more than once')
+    else:
+        print(f'In {txt1} no character appears more than once')
+
+    txt2 = "pear"
+    result = duplicates_has(txt2)
+    if result:
+        print(f'In {txt2} {result} appears more than once')
+    else:
+        print(f'In {txt2} no character appears more than once')
+
+main_6ex()