Intersection of Sorted Posting Lists

Problem Given multiple sorted lists of document IDs (postings), return the IDs present in all of them.

Input / Output

• Input: k sorted integer lists of document IDs.
• Output: the sorted list of IDs that appear in every input list.

Constraints

• Lists can be large; aim for a single linear merge rather than repeated membership tests.
• IDs within each list are strictly increasing.

Example

• [1,2,4,8], [2,4,9], [2,4,5] → [2,4]