Code Explanation:
🔹 1. Importing deque
from collections import deque
✅ Explanation:
deque stands for Double Ended Queue.
It is available in Python's collections module.
It allows fast insertion and deletion from both ends.
Think of it like:
Front ← [ deque ] → Back
🔹 2. Creating a Deque with Maximum Size
d = deque(maxlen=3)
✅ Explanation:
An empty deque is created.
But:
maxlen = 3
means:
Maximum 3 elements can be stored
Current state:
deque([])
Visual:
Capacity = 3
[ ]
🔹 3. Using extend()
d.extend([1, 2, 3, 4])
✅ Explanation:
extend() inserts all elements one by one from the list.
Python processes:
[1, 2, 3, 4]
sequentially.
🔹 4. Insert First Element
1
Deque becomes:
[1]
Current size:
1/3
🔹 5. Insert Second Element
2
Deque becomes:
[1, 2]
Current size:
2/3
🔹 6. Insert Third Element
3
Deque becomes:
[1, 2, 3]
Current size:
3/3
Deque is now full.
🔹 7. Insert Fourth Element
4
✅ Explanation:
Now deque already contains:
[1, 2, 3]
and capacity is:
3
When 4 is inserted:
[1, 2, 3, 4]
would exceed capacity.
So deque automatically removes the oldest element from the left.
Removed:
1
New deque:
[2, 3, 4]
🔹 8. Final State
After all insertions:
deque([2, 3, 4], maxlen=3)
Visual:
Front
↓
[2, 3, 4]
↑
Back
🔹 9. Convert to List
list(d)
✅ Explanation:
Converts deque into a normal Python list.
Before:
deque([2, 3, 4])
After:
[2, 3, 4]
🔹 10. Print Result
print(list(d))
Prints:
[2, 3, 4]
🎯 Final Output
[2, 3, 4]
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