![]() (In a more technical sense, we say that the amortized cost of removing an element from the end is O(1)). ![]() However, you can show that these resizes are sufficiently infrequent that the average cost of doing a remove from the end is O(1). If that happens, then yes, you'll need to make a new array, copy over the old elements, and free the previous array, which does take time O(n). In many implementations of dynamic arrays, you'll sometimes need to perform resize operations to make sure that the size of the allocated array is within some constant factor of the number of elements. You are absolutely right that you can just destroy the object at the final position in a dynamic array and then decrement the size to remove the last element. In that case, from a worst-worst-case perspective, you could say that the complexity is O(n) because reducing the size involves copying n elements to the reduced array.Īlthough it's not true for Java ArrayList implementations, when the author of this book talks about "dynamic arrays" that "reduce the array size" on deletion when necessary, then the worst-case complexity of a delete at the end of the array is indeed O(n). But the author is talking about (or believes that ArrayList does) reduce the array size. Half if the elements in the array are less than half.Ī Java ArrayList doesn't do this - it doesn't decrease in storage when elements are removed. Note: We will see the implementation for dynamic array in the Stacks, Queues and Hashing chapters.įrom this we learn that array lists are examples of a "Dynamic Array" as the author of the book defines it.īut looking further, the book mentioned that:Īs soon as that array becomes full, create the new array of sizeĭouble than the original array. ![]() ![]() First, let's look up what the books means with a "Dynamic Array":ĭynamic array (also called as growable array, resizable array,ĭynamic table, or array list) is a random access, variable-size list data structure that allows elements to be added or removed. ![]()
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