diff --git a/dsa/d3/exercise_4.py b/dsa/d3/exercise_4.py
new file mode 100644
index 0000000..ab8780d
--- /dev/null
+++ b/dsa/d3/exercise_4.py
@@ -0,0 +1,24 @@
+def main():
+    s = "race a car"
+    print(palindrome(s))
+
+def palindrome(s):
+    clean_s = ""
+
+    for x in s:
+        if x.isalpha() or x.isdigit():
+            clean_s+=x.lower()
+    if not clean_s:
+        return False
+
+    left = 0
+    right = len(clean_s)-1
+
+    while left<right:
+        if clean_s[left] != clean_s[right]:
+            return False
+        left+=1
+        right-=1
+    return True
+
+if __name__ == "__main__": main()
\ No newline at end of file
diff --git a/dsa/d3/exercise_5.py b/dsa/d3/exercise_5.py
new file mode 100644
index 0000000..29d151b
--- /dev/null
+++ b/dsa/d3/exercise_5.py
@@ -0,0 +1,17 @@
+def main():
+    s = "race e car"
+    print(palindrome(s))
+
+def palindrome(s):
+    cleaned = "".join(ch.lower() for ch in s if ch.isdigit() or ch.isalpha())
+    left = 0
+    right=len(cleaned)-1
+
+    while left<right:
+        if cleaned[left]!=cleaned[right]:
+            return False
+        left+=1
+        right-=1
+    return True
+
+if __name__ == "__main__": main()
\ No newline at end of file
diff --git a/dsa/d4/exercise_7.py b/dsa/d4/exercise_7.py
new file mode 100644
index 0000000..84d44f4
--- /dev/null
+++ b/dsa/d4/exercise_7.py
@@ -0,0 +1,27 @@
+def main():
+    nums = [-2, 1, -3, 4, -1, 2, 1, -5, 4]  # → [4, -1, 2, 1]
+    print(kadane_algorithm(nums))
+
+def kadane_algorithm(nums):
+    current_sum = nums[0]
+    max_sum=nums[0]
+    temp_start=0
+    best_start=0
+    best_end=0
+
+    for i in range(1, len(nums)):
+
+        if current_sum + nums[i]>nums[i]:
+            current_sum=current_sum+nums[i]
+        else:
+            current_sum=nums[i]
+            temp_start=i
+
+        if current_sum>max_sum:
+            max_sum=current_sum
+            best_start=temp_start
+            best_end=i
+
+    return nums[best_start:best_end+1]
+
+if __name__ == "__main__": main()
diff --git a/dsa/d5/exercise_6.py b/dsa/d5/exercise_6.py
new file mode 100644
index 0000000..4a94a98
--- /dev/null
+++ b/dsa/d5/exercise_6.py
@@ -0,0 +1,18 @@
+from collections import defaultdict
+
+
+def main():
+    words = ["eat", "tea", "tan", "ate", "nat", "bat"]
+    print(group_anagram(words))
+
+def group_anagram(words):
+
+    result = defaultdict(list)
+
+    for word in words:
+        key="".join(sorted(word))
+        result[key].append(word)
+    return dict(result)
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file
diff --git a/dsa/e1/exercise_5.py b/dsa/e1/exercise_5.py
new file mode 100644
index 0000000..2ea6ea7
--- /dev/null
+++ b/dsa/e1/exercise_5.py
@@ -0,0 +1,14 @@
+def main():
+    string = 'eceba'
+    k = 2
+    print(longest_k_distinct(string,k))
+
+def longest_k_distinct(string, k):
+
+    left=0
+    right=0
+    count ={}
+    for right in range(len(string)):
+        count[string[right]] = count.get(string[right], 0) + 1
+        while len(count) > k:
+            count[right]-=1
\ No newline at end of file
diff --git a/dsa/e1/exercise_6.py b/dsa/e1/exercise_6.py
new file mode 100644
index 0000000..78f43e5
--- /dev/null
+++ b/dsa/e1/exercise_6.py
@@ -0,0 +1,27 @@
+def main():
+    string = 'eceba'
+    k = 2
+    print(longest_k_distinct(string,k))
+
+def longest_k_distinct(s, k):
+    left=0
+    seen={}
+    max_length=0
+    best_start=0
+    for right in range(len(s)):
+        seen[s[right]] = seen.get(s[right],0)+1
+
+        while len(seen) > k:
+            seen[s[left]]-=1
+
+            if seen[s[left]]==0:
+                del seen[s[left]]
+            left+=1
+
+        if right - left + 1 > max_length:
+            max_length = right - left + 1
+            best_start = left
+
+    return s[best_start:best_start+max_length]
+
+if __name__ == "__main__": main()
\ No newline at end of file
diff --git a/dsa/e2/exercise_4.py b/dsa/e2/exercise_4.py
new file mode 100644
index 0000000..4a2f700
--- /dev/null
+++ b/dsa/e2/exercise_4.py
@@ -0,0 +1,17 @@
+def main():
+    a = [3,1,4,1,5]
+    b = [1,5,9,1]
+    print(ordered_intersection(a,b))
+
+def ordered_intersection(a,b):
+    in_b = set(b)
+    added=set()
+    result=[]
+
+    for x in a:
+        if x not in added and x in in_b:
+            added.add(x)
+            result.append(x)
+    return result
+
+if __name__ == "__main__": main()
\ No newline at end of file
diff --git a/dsa/e3/exercise_6.py b/dsa/e3/exercise_6.py
new file mode 100644
index 0000000..7148812
--- /dev/null
+++ b/dsa/e3/exercise_6.py
@@ -0,0 +1,28 @@
+from collections import defaultdict
+
+
+def main():
+    logs = [
+        "ivan,login,09:00", "ivan,upload,09:05", "ivan,login,09:10",
+        "maria,login,09:02", "maria,delete,09:06", "maria,upload,09:07",
+        "BAD",
+        "georgi,login,09:20",
+    ]
+    print(most_versatile_user(logs))
+
+def most_versatile_user(logs):
+    versatile_users = defaultdict(set)
+    for log in logs:
+        try:
+            user, action, date = log.split(",")
+        except (AttributeError, ValueError):
+            continue
+        else:
+            versatile_users[user].add(action)
+    if not versatile_users:
+        return None
+    user = min(versatile_users, key=lambda u:(-len(versatile_users[u]), u))
+    return user, len(versatile_users[user])
+
+if __name__ == "__main__":
+    main()
diff --git a/dsa/e3/exercise_7.py b/dsa/e3/exercise_7.py
new file mode 100644
index 0000000..e0e10e6
--- /dev/null
+++ b/dsa/e3/exercise_7.py
@@ -0,0 +1,30 @@
+from collections import defaultdict
+
+
+def main():
+    logs = [
+        "ivan,login,09:00", "ivan,upload,09:05", "ivan,login,09:10",
+        "maria,login,09:02", "maria,delete,09:06", "maria,upload,09:07",
+        "BAD",
+        "georgi,login,09:20",
+    ]
+    print(most_versatile_user(logs))
+
+def most_versatile_user(logs):
+
+    versatile_users=defaultdict(set)
+    for log in logs:
+        try:
+            user,action,time=log.split(",")
+        except (AttributeError, ValueError):
+            continue
+        else:
+            versatile_users[user].add(action)
+
+    if not versatile_users:
+        return None
+
+    user = max(versatile_users, key=lambda u:len(versatile_users[u]))
+    return user, len(versatile_users[user])
+
+if __name__ == "__main__": main()
diff --git a/dsa/e4/exercise_5.py b/dsa/e4/exercise_5.py
new file mode 100644
index 0000000..7e0e64c
--- /dev/null
+++ b/dsa/e4/exercise_5.py
@@ -0,0 +1,31 @@
+def main():
+    a = [1,3,5]
+    b = [2,4,6]
+    print(merge_sorted(a,b))
+
+def merge_sorted(a,b):
+
+    result =[]
+    left=0
+    right=0
+
+    while left<len(a) and right<len(b):
+        if a[left] < b[right]:
+            result.append(a[left])
+            left+=1
+        else:
+            result.append(b[right])
+            right+=1
+
+    while left<len(a):
+        result.append(a[left])
+        left+=1
+
+    while right<len(b):
+        result.append(b[right])
+        right+=1
+
+    return result
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file
diff --git a/exercise/decorator/exercise_1.py b/exercise/decorator/exercise_1.py
index 7bdbd08..5693323 100644
--- a/exercise/decorator/exercise_1.py
+++ b/exercise/decorator/exercise_1.py
@@ -51,5 +51,20 @@ def wrapper(*args, **kwargs):
 def get_ice_cream(flavor):
     print(f"Here is your {flavor} ice cream 🍨")
 
-get_ice_cream("chocolate")
+#get_ice_cream("chocolate")
+
+def timer(func):
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        start = time.perf_counter()
+        result = func(*args, **kwargs)
+        print(f"{func.__name__} took {time.perf_counter() - start:.4f}s")
+        return result
+    return wrapper
+
+@timer
+def slow_sum(n):
+    return sum(range(n))
+
+print(slow_sum(5))
 
diff --git a/hashing/task1/exercise_1.py b/hashing/task1/exercise_1.py
index ca0183b..6bc0d00 100644
--- a/hashing/task1/exercise_1.py
+++ b/hashing/task1/exercise_1.py
@@ -4,7 +4,6 @@ def main():
     output = first_none_repeating(user_input)
     print(output)
 
-
 def first_none_repeating(s: str):
     if s is None or s == "":
         return '_'
diff --git a/movie_catalog_parser/exercise_1.py b/movie_catalog_parser/exercise_1.py
new file mode 100644
index 0000000..395fe5b
--- /dev/null
+++ b/movie_catalog_parser/exercise_1.py
@@ -0,0 +1,98 @@
+from collections import defaultdict
+
+class InvalidMovieError(Exception): pass
+
+class Movie:
+
+    def __init__(self,title, genre, rating, votes):
+        self.title =title
+        self.genre=genre
+        self.rating=rating
+        self.votes=votes
+
+    def __repr__(self):
+        return f"{self.title} ({self.rating})"
+
+
+    @classmethod
+    def from_line(cls, line):
+        try:
+            title, genre, rating, votes=line.split(",")
+            rating = float(rating)
+            votes=int(votes)
+        except ValueError:
+            raise InvalidMovieError("Invalid movie")
+
+        if not 0<=rating<=10:
+            raise InvalidMovieError("Invalid rating")
+
+        return cls(title.strip(), genre.strip(), rating, votes)
+
+
+
+class Catalog:
+    def __init__(self):
+        self.movies=[]
+
+    def add_movie(self, movie):
+        self.movies.append(movie)
+
+    def average_rating_by_genre(self):
+        genre_ratings=defaultdict(list)
+        for movie in self.movies:
+            genre_ratings[movie.genre].append(movie.rating)
+        result = {}
+        for genre, rating in genre_ratings.items():
+            result[genre] = round(sum(rating)/len(rating), 2)
+        return result
+
+    def top_rated(self, n):
+        return sorted(
+            self.movies,
+            key=lambda movie: (-movie.rating, movie.title)
+        )[:n]
+
+    def most_voted(self):
+        return max(self.movies, key=lambda m:m.votes)
+
+    def genres(self):
+        genres=[]
+        added=[]
+        for m in self.movies:
+            if m.genre not in added:
+                added.append(m.genre)
+                genres.append(m.genre)
+        return sorted(genres)
+        #return sorted(set(m.genre for m in self.movies))
+
+def read_from_file(file_name):
+    lines=[]
+    try:
+        with open(file_name, "r") as f:
+            lines = f.readlines()
+    except FileNotFoundError:
+        print("File not found")
+        return []
+    else:
+        return lines
+
+def main():
+    catalog = Catalog()
+    lines = read_from_file("sample.txt")
+    skipped=0
+
+    for line in lines:
+        if not line.strip():
+            continue
+        try:
+            catalog.add_movie(Movie.from_line(line.strip()))
+        except InvalidMovieError:
+            skipped+=1
+    print(f"Skipped {skipped} malformed lines")
+    print(f"Average rating by genre: {catalog.average_rating_by_genre()}")
+    print(f"Top rated: {catalog.top_rated(3)}")
+    print(f"Most voted: {catalog.most_voted()}")
+    print(f"Genres: {catalog.genres()}")
+
+if __name__ == "__main__":
+    main()
diff --git a/movie_catalog_parser/sample.txt b/movie_catalog_parser/sample.txt
new file mode 100644
index 0000000..9939c8f
--- /dev/null
+++ b/movie_catalog_parser/sample.txt
@@ -0,0 +1,9 @@
+Inception,SciFi,8.8,2000000
+The Room,Drama,3.7,150000
+Interstellar,SciFi,8.6,1500000
+Parasite,Thriller,8.5,800000
+BadRating,Drama,12.5,1000
+Cats,Musical,2.8,50000
+Whiplash,Drama,8.5,700000
+Broken,SciFi,notanumber,500
+Tenet,SciFi,7.4
\ No newline at end of file
diff --git a/movie_catalog_parser/task b/movie_catalog_parser/task
new file mode 100644
index 0000000..617b937
--- /dev/null
+++ b/movie_catalog_parser/task
@@ -0,0 +1,41 @@
+Here's the harder version — new domain, and it adds the three things that push it to the top of the intern range: grouping + average, sorting with a tie-break, and validation beyond just type conversion. Read the spec carefully (there's a validation rule that's easy to miss), write it, run it against the expected output, then send it. After I review the code, I'll ask you the complexity follow-ups — same as a real interview.
+
+Task: Movie Catalog Parser
+Each line describes a movie:
+
+Requirements:
+
+Movie class: title, genre, rating (float), votes (int).
+from_line(line) classmethod. Raise InvalidMovieError if a line is malformed OR if the rating is not between 0 and 10 (inclusive). ← don't miss this validation rule.
+Catalog class holding movies, with:
+average_rating_by_genre() → dict of genre → average rating of movies in that genre (rounded to 2 decimals).
+top_rated(n) → list of the top n movies by rating, highest first; when ratings tie, order by title A→Z.
+most_voted() → the movie with the most votes.
+genres() → a sorted list of the unique genres.
+Parse the lines, skip malformed ones, count them, and print the report.
+Sample input
+Inception,SciFi,8.8,2000000
+The Room,Drama,3.7,150000
+Interstellar,SciFi,8.6,1500000
+Parasite,Thriller,8.5,800000
+BadRating,Drama,12.5,1000
+Cats,Musical,2.8,50000
+Whiplash,Drama,8.5,700000
+Broken,SciFi,notanumber,500
+Tenet,SciFi,7.4
+
+(Three should be skipped: BadRating rating out of range, Broken bad rating, Tenet missing a field.)
+
+Expected output
+Skipped 3 malformed lines
+Average rating by genre: {'SciFi': 8.7, 'Drama': 6.1, 'Thriller': 8.5, 'Musical': 2.8}
+Top rated: Inception (8.8), Interstellar (8.6), Parasite (8.5)
+Most voted: Inception (2000000)
+Genres: ['Drama', 'Musical', 'SciFi', 'Thriller']
+
+What's harder here (what I'm testing)
+Grouping + average: you need to collect ratings per genre and average them — think defaultdict(list) then average, or accumulate sum+count.
+Sorting with a tie-break: top_rated needs rating descending and title ascending on ties — one sort key with mixed directions. (This is the tuple-key thing.)
+Validation logic: the rating range check (0–10) is a rule beyond type conversion — easy to skip if you don't read carefully.
+Uniqueness + sorting: genres() = unique, then sorted.
+Take your time, run it, compare to the expected output, then send it. I'll review, then hit you with the complexity questions.
\ No newline at end of file
diff --git a/product_inventory_parser/exercise_1.py b/product_inventory_parser/exercise_1.py
new file mode 100644
index 0000000..67b1fad
--- /dev/null
+++ b/product_inventory_parser/exercise_1.py
@@ -0,0 +1,78 @@
+from collections import Counter
+
+class InvalidProductError(Exception): pass
+
+class Product:
+
+    def __init__(self, name, category, price, quantity):
+        self.name=name
+        self.category=category
+        self.price=price
+        self.quantity=quantity
+
+    @classmethod
+    def from_line(cls, line):
+        try:
+            name,category,price,quantity=line.split(",")
+            price=float(price)
+            quantity=int(quantity)
+        except ValueError:
+            raise InvalidProductError("Invalid product")
+        else:
+            return cls(name.strip(),category.strip(),price,quantity)
+
+    def __str__(self):
+        return f"Name: {self.name}, Category: {self.category}, Price: {self.price}, Quantity: {self.quantity}"
+
+class Inventory:
+
+    def __init__(self):
+        self.products = []
+
+    def add_product(self, product):
+        self.products.append(product)
+
+    def total_value(self):
+        return round(sum((p.price * p.quantity) for p in self.products), 2)
+
+    def count_by_category(self):
+        return dict(Counter(p.category for p in self.products))
+
+    def most_expensive(self):
+        if not self.products:
+            return None
+        return max(self.products, key=lambda p:p.price)
+
+    def __repr__(self):
+        return f"Inventory: {self.products}"
+
+def read_from_file(filename):
+    lines=[]
+    try:
+        with open(filename, "r") as f:
+            lines = f.readlines()
+    except FileNotFoundError:
+        print("File couldn't find")
+        return []
+    else:
+        return lines
+
+def main():
+    lines = read_from_file("sample.txt")
+    skipped=0
+    inventory = Inventory()
+    for line in lines:
+        if not line.strip():
+            continue
+        try:
+            inventory.add_product(Product.from_line(line.strip()))
+        except InvalidProductError:
+            skipped+=1
+    print(f"Skipped {skipped} malformed lines")
+    print(f"Total value: {inventory.total_value():.2f}")
+    print(f"Count by category: {inventory.count_by_category()}")
+    print(f"Most expensive: {inventory.most_expensive()}")
+
+
+if __name__ == "__main__": main()
+
diff --git a/product_inventory_parser/sample.txt b/product_inventory_parser/sample.txt
new file mode 100644
index 0000000..73eea3c
--- /dev/null
+++ b/product_inventory_parser/sample.txt
@@ -0,0 +1,7 @@
+Laptop,Electronics,899.99,3
+Mouse,Electronics,19.99,10
+Desk,Furniture,149.50,5
+Chair,Furniture,89.00,8
+BrokenLine,Electronics,notanumber,2
+Monitor,Electronics,199.99
+Keyboard,Electronics,49.99,7
\ No newline at end of file
diff --git a/searching_sorting/binary_search/exercise_7.py b/searching_sorting/binary_search/exercise_7.py
new file mode 100644
index 0000000..11ae4c6
--- /dev/null
+++ b/searching_sorting/binary_search/exercise_7.py
@@ -0,0 +1,21 @@
+def main():
+    nums = [1, 3, 5, 7, 9, 11]
+    target = 7
+    print(binary_search(nums,target))
+
+def binary_search(nums,target):
+
+    left=0
+    right=len(nums)-1
+
+    while left<=right:
+        mid = left + right+left // 2
+        if nums[mid] == target:
+            return mid
+        elif nums[mid] > target:
+            right = mid-1
+        else:
+            left = mid+1
+    return -1
+
+if __name__ == "__main__": main()
\ No newline at end of file
diff --git a/searching_sorting/bubble_sort/exercise_6.py b/searching_sorting/bubble_sort/exercise_6.py
new file mode 100644
index 0000000..ed6fc04
--- /dev/null
+++ b/searching_sorting/bubble_sort/exercise_6.py
@@ -0,0 +1,17 @@
+def main():
+    nums = [5, 1, 4, 2, 8]
+    print(bubble_sort(nums))
+
+def bubble_sort(nums):
+
+    for i in range(len(nums)):
+        swapped = False
+        for j in range(len(nums)-1-i):
+            if nums[j] > nums[j+1]:
+                nums[j], nums[j+1] = nums[j+1], nums[j]
+                swapped=True
+        if not swapped:
+            break
+    return nums
+
+if __name__ == "__main__":main()
\ No newline at end of file
diff --git a/sliding_window/task3/exercise_8.py b/sliding_window/task3/exercise_8.py
new file mode 100644
index 0000000..dac6718
--- /dev/null
+++ b/sliding_window/task3/exercise_8.py
@@ -0,0 +1,23 @@
+def main():
+    s = "babad"
+    print(longest_non_repeating_substring(s))
+
+def longest_non_repeating_substring(s):
+    left = 0
+    seen = set()
+    max_length=0
+    best_start=0
+    for right in range(len(s)):
+        while s[right] in seen:
+            seen.remove(s[left])
+            left+=1
+        seen.add(s[right])
+        if max_length<right-left+1:
+            max_length=right-left+1
+            best_start=left
+    return s[best_start:best_start+max_length]
+
+
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file
diff --git a/stack_queue/task1/exercise_5.py b/stack_queue/task1/exercise_5.py
new file mode 100644
index 0000000..b4b2a22
--- /dev/null
+++ b/stack_queue/task1/exercise_5.py
@@ -0,0 +1,23 @@
+def main():
+    s = "{[()]}"
+    print(is_valid_parentheses(s))
+
+def is_valid_parentheses(s):
+    pairs={")":"(", "]":"[", "}":"{"}
+    stack = []
+
+    for i in range(len(s)):
+        #opening
+        if s[i] in pairs.values():
+            stack.append(s[i])
+
+        #closing
+        if s[i] in pairs:
+            if not stack:
+                return False
+            if stack.pop() != pairs[s[i]]:
+                return False
+    return len(stack) == 0
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file