What is the principle of a hashmap?

A hashmap is a data structure used to store key-value pairs, which achieves fast lookups by mapping keys to positions in a hash table. The specific principle is as follows:

1. When we insert a key-value pair into a hashmap, the index position of the key in the hash table is first calculated based on the hash value of the key.
2. If the index location is empty, store the key-value pair directly in that location.
3. If another key-value pair already exists at the index location, a hash collision may occur (where different keys have the same hash value), typically resolved using open addressing or chaining to address the collision issue.
4. When using open addressing, in case of a collision, a certain probing sequence will be used to find the next available slot until an empty slot is found to store the key-value pair.
5. When using chaining in hashing, if there is a collision, key-value pairs with the same hash value will be stored in the same location and organized into a linked list or other data structure to store conflicting key-value pairs.

Hashmap achieves fast insertion, retrieval, and deletion operations with high efficiency through the use of hashing algorithms and conflict resolution methods.