s0128_longest_consecutive_sequence

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

import scala.util.Sorting.quickSort

object Solution {
    def longestConsecutive(nums: Array[Int]): Int = {
        if (nums.isEmpty) {
            return 0
        }

        quickSort(nums)
        var max = Int.MinValue
        var thisMax = 1

        for (i <- 0 until nums.length - 1) {
            if (nums(i + 1) == nums(i) + 1) {
                thisMax += 1
            } else if (nums(i + 1) != nums(i)) {
                max = Math.max(max, thisMax)
                thisMax = 1
            }
        }

        Math.max(max, thisMax)
    }
}