LeetCode-in-All
128. Longest Consecutive Sequence
Medium
Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
You must write an algorithm that runs in O(n) time.
Example 1:
Input: nums = [100,4,200,1,3,2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
Example 2:
Input: nums = [0,3,7,2,5,8,4,6,0,1]
Output: 9
Constraints:
0 <= nums.length <= 105-109 <= nums[i] <= 109
Solution
-spec longest_consecutive(Nums :: [integer()]) -> integer().
longest_consecutive(Nums) ->
Sorted = lists:sort(Nums),
SeqLens = count_consecutive(Sorted, [1]),
lists:max(SeqLens).
-spec count_consecutive(Nums :: [integer()], SeqLens :: [integer()]) -> [integer()].
count_consecutive([H1, H2 | Tail], [SeqHead | SeqTail]) ->
NewLen = case H1 - H2 of
-1 -> SeqHead + 1; % Consecutive elements
0 -> SeqHead; % Same element, do nothing
_ -> 1 % Not consecutive, reset count
end,
count_consecutive([H2 | Tail], [NewLen | [SeqHead | SeqTail]]);
count_consecutive([_], SeqLens) ->
SeqLens; % End of list with remaining sequence lengths
count_consecutive([], [_]) ->
[0]. % Single number case