Longest Consecutive Sequence

Write `longest_consecutive(nums)` returning the length of the longest run of consecutive integers present in the list. The values are unsorted and may repeat. longest_consecutive([100, 4, 200, 1, 3, 2]) -> 4 (1, 2, 3, 4) Sorting gives O(n log n) and is worth mentioning before you discard it. For O(n): put everything in a set, and only start counting upward from a value whose predecessor is absent. That guard is what makes the whole thing linear rather than quadratic — be ready to prove it, because it is the follow-up.