What is the main idea behind the HashMap data structure?

The main idea of the HashMap data structure is to store key-value pairs with efficient insertion, search, and deletion of elements.

HashMap uses a hash function to convert the key into an array index (bucket). Elements with the same hash (collisions) are usually stored in a linked list or a balanced tree within the bucket.

When adding or searching for an element, HashMap computes the hash of the key, finds the corresponding bucket, and then searches for the element inside it. This allows operations to be performed on average in O(1) time.

Example:

Map<String, Integer> map = new HashMap<>();
map.put("apple", 3);
int count = map.get("apple"); // quickly retrieves the value by key