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 java.util.PriorityQueue

class Solution {
    fun longestConsecutive(nums: IntArray): Int {
        if (nums.isEmpty()) {
            return 0
        }
        val queue = PriorityQueue<Int>()
        nums.forEach {
            queue.add(it)
        }
        var lastNum = Integer.MIN_VALUE
        var length = 0
        var maxLength = 1
        while (queue.isNotEmpty()) {
            val num = queue.poll()
            if (num == lastNum) {
                continue
            }
            length++
            if (num - lastNum > 1) {
                length = 1
            }
            lastNum = num
            maxLength = maxOf(maxLength, length)
        }
        return maxLength
    }
}