PreCourse 1 Completed

[CHINMAY-PRAJAPATI]

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[super30admin]

Overall, your solutions demonstrate a good understanding of the data structures. However, there are several areas for improvement:

1. Exercise_1.py (Stack using list):

   • Correctness: The stack operations are implemented correctly. However, the pop and peek methods return a string "Stack is Empty" when the stack is empty. This can cause type errors if the stack is expected to return a specific type (like integer). Consider raising an exception (like IndexError) or returning None instead.
   • Time Complexity: You correctly identified that push and pop are O(1). However, the space complexity is O(n) because the list grows with the number of elements. You wrote O(1) which is incorrect.

2. Exercise_2.py (Stack using linked list):

   • Correctness: The stack implementation is correct. However, the test code has an issue: when popping, it tries to convert the popped value to an integer (int(popped)), but if the stack is empty, popped is None, which causes a TypeError. You should avoid converting to int in the test code if the value might be None.
   • Time Complexity: You correctly identified O(1) for push and pop, and O(n) for show. But the space complexity is O(n) for the entire stack (each node uses memory), not O(1).

3. Exercise_3.py (Singly linked list):

   • Correctness: The append method works correctly. The find method returns a string "Found the matching key" when found, which is not typical. Usually, we return the node or the data. Similarly, remove returns a string when successful. Consider returning the removed data or a boolean indicating success.
   • The remove method has a bug: if the head is to be removed, it does so correctly. But if the list has only one node (the head) and we remove it, then the head becomes None. However, in your code, you set self.head = self.head.next which is correct. But note: your code uses two pointers, but in the case of removing the head, you don't need the two-pointer technique. Your code handles it.
   • However, in remove, you have a while loop that checks current is not None. Inside, you check if current.data == key. Then you check if current == self.head. This is correct for removing the head. But what if the key is not in the list? You traverse until the end and return None. This is correct.
   • Time Complexity: You correctly identified O(n) for append, find, and remove. But the space complexity is O(n) for the entire list, not O(1).

General:

• Always ensure that the return types of methods are consistent and meaningful. Avoid returning strings for methods that should return data.
• Be accurate in your complexity analysis: space complexity should consider the memory used by the data structure, which is typically O(n) for these structures.

Keep up the good work, and focus on these improvements.