Can you list the types of indexes used in data structures?

Different types of indexes are used in data structures and databases to speed up search and data access:

• Hash indexes — use hash functions for quick key-based access, effective for exact searches.
• B-trees (B-Tree) — balanced trees, often used in DBMS for range queries and sorting.
• B+ trees (B+ Tree) — a variant of B-trees with additional links between leaf nodes for efficient traversal.
• Bitmap indexes — use bitmaps for fast filtering based on low-cardinality values.
• Full-text indexes — for quick text search.
• R-trees — for indexing spatial data (e.g., geospatial data).

In PHP, for example, arrays are implemented as hash tables, which provide fast key-based access.