Explain Huffman coding and its greedy approach.

Huffman coding creates optimal prefix-free codes for lossless compression. Greedy approach: build binary tree bottom-up by repeatedly combining two lowest-frequency nodes. Frequent characters get shorter codes, rare characters get longer codes. Use min-heap to efficiently find minimum nodes. Time O(n log n). Guarantees optimal prefix code where no code is prefix of another. Used in ZIP, JPEG, MP3 compression.