Milline on HashMap-i elementide operatsioonide ajakulud ning kas HashMap tagab nimetatud keerukuse elemendi valimisel?

The time complexity of core operations (get, put, remove, containsKey) in HashMap is on average O(1).

This is achieved through the use of a hash table, where elements are stored in cells (buckets) determined by the hash code of the key. In an ideal case, each bucket contains only one element.

However, in the worst case, when all keys have the same hash code or there are many collisions, elements fall into the same bucket. In this case, the bucket can turn into a linked list (up to Java 8) or a tree (Java 8 and above, if the number of elements in the bucket exceeds a certain threshold). Operations on such a bucket have a time complexity of O(n), where n is the number of elements in the bucket.

HashMap does not guarantee constant time O(1) for element retrieval. It guarantees only an average time complexity of O(1). In the worst case, the complexity can be O(n).

Factors affecting time complexity:

• Quality of the hash function: A good hash function distributes keys evenly across buckets, minimizing collisions.
• load factor (load coefficient): Determines how full the hash table can be before its size is increased (rehash). A high load factor can increase the likelihood of collisions.
• Initial capacity: Too small an initial capacity with a large number of elements will cause frequent rehashes, which are resource-intensive operations.