LeetCode 900. RLE Iterator

Implement an iterator over a run-length encoded sequence represented as an array of (count, value) pairs. Support a next(n) operation that exhausts the next n elements by advancing through the encoded pairs and returns the last element exhausted, or -1 if there are no more elements. The solution must maintain state across calls and efficiently handle large values of n by skipping/consuming counts without decoding the full sequence.