What is "element shifting" and why is it inefficient?

Element shifting is an operation in which, after the first element of an array is removed, all the remaining ones move one position forward to fill the freed space.

For example, if there was a queue [A, B, C, D], and A is removed, the array becomes [B, C, D]: this requires physically shifting all elements by one position.

Why this is inefficient:

• Every removal requires moving all the remaining elements,
• This takes O(n) time, where n is the number of elements,
• With large amounts of data, such shifts drastically slow the program down.

That is why, instead of a plain array, queues are implemented using:

• a circular buffer (indexes "wrap around" cyclically),
• or a linked list, where removal and addition happen in O(1) without shifting.