Explain the Rabin-Karp algorithm for string matching.

Rabin-Karp uses rolling hash to find pattern in text. Compute hash of pattern and first window of text. Slide window, updating hash in O(1) using rolling hash: remove contribution of outgoing char, add incoming char. When hashes match, verify with character comparison (to handle hash collisions). Average O(n+m) time but O(nm) worst case. Efficient for multiple pattern search.