Implement queue and parentheses validator

custom_queue.py

@@ -2,29 +2,44 @@
 
 class Queue:
     def __init__(self):
-        self.items = []
+         self.items = []
 
     def enqueue(self, item):
-        # TODO: Add an item to the end of the queue
-        pass
+        # Add an item to the end of the queue
+        self.items.append(item)
 
     def dequeue(self):
-        # TODO: Remove and return the item from the front of the queue
-        pass
+        # Remove and return the item from the front of the queue
+        if self.is_empty():
+            return None
+        return self.items.pop(0)
+
 
     def peek(self):
-        # TODO: Return the item at the front of the queue without removing it
-        pass
+        # Return the item at the front of the queue without removing it
+        if self.is_empty():
+            return None
+        return self.items[0]
 
     def is_empty(self):
-        # TODO: Return True if the queue is empty
-        pass
+        # Return True if the queue is empty
+        return len(self.items) == 0
 
     def select_and_announce_winner(self):
         """
         Randomly selects a winner from the queue.
         Dequeues all items up to and including the winner.
         Returns the name of the winning customer.
         """
-        # TODO: Implement winner selection and dequeue process
-        pass
+        if self.is_empty():
+            return None
+
+        # choose a random index
+        winner_index = random.randint(0, len(self.items) - 1)
+        winner = self.items[winner_index]
+
+        # remove everyone up to and including the winner
+        for _ in range(winner_index + 1):
+            self.dequeue()
+
+        return winner

custom_stack.py

@@ -4,4 +4,31 @@ def is_valid_parentheses(s: str) -> bool:
     Only (), {}, and [] are considered valid.
     """
     # TODO: Implement stack logic to validate parentheses
-    pass
+    stack = []  #  store opening brackets
+
+    # dictionary to match closing to opening brackets
+    matches = {
+        ")": "(",
+        "}": "{",
+        "]": "["
+    }
+
+    # go through each character in the string
+    for char in s:
+        if char in "({[":
+            # push opening brackets onto the stack
+            stack.append(char)
+        elif char in ")}]":
+            # if there's no opening bracket to match
+            if len(stack) == 0:
+                return False
+
+            # pop the last opening bracket
+            top = stack.pop()
+
+            # check if it matches the current closing bracket
+            if top != matches[char]:
+                return False
+
+    # if stack is empty, all brackets were matched
+    return len(stack) == 0