Last updated on October 5th, 2024 at 05:28 pm

Here, We see Longest Consecutive Sequence LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

List of all LeetCode Solution

Longest Consecutive Sequence LeetCode Solution

Problem Statement

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

1. Longest Consecutive Sequence LeetCode Solution C++

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        int n = nums.size();
        if(n == 0){
            return 0;
        }
        sort(nums.begin(), nums.end());
        int currentConsecutiveSequence = 1;
        int longestConsecutiveSequence = 0;
        for(int i=1; i<n; i++){
            if(nums[i] != nums[i-1]){
                if(nums[i] == nums[i-1] + 1){
                    currentConsecutiveSequence++;
                }
                else{
                    longestConsecutiveSequence = max(longestConsecutiveSequence, currentConsecutiveSequence);
                    currentConsecutiveSequence = 1;
                }
            }
        }
        return max(longestConsecutiveSequence, currentConsecutiveSequence);
    }
};

2. Longest Consecutive Sequence LeetCode Solution Java

class Solution {
    public int longestConsecutive(int[] nums) {int result = 0;
        if (nums.length > 0) {
            if (nums.length < 1000) {
                Arrays.sort(nums);
                int current = 0;
                for (int i = 1; i < nums.length; i++) {
                    if (nums[i] != nums[i - 1]) {
                        if (nums[i] - nums[i - 1] == 1) {
                            current++;
                        } else {
                            if (current + 1 > result) {
                                result = current + 1;
                            }
                            current = 0;
                        }
                    }
                }
                if (current + 1 > result) {
                    result = current + 1;
                }
            } else {
                int min = Integer.MAX_VALUE;
                int max = Integer.MIN_VALUE;
                for (int num : nums) {
                    if (num > max) {
                        max = num;
                    }
                    if (num < min) {
                        min = num;
                    }
                }
                byte[] bits = new byte[max - min + 1];
                for (int num : nums) {
                    bits[num - min] = 1;
                }
                int current = 0;
                for (byte bit : bits) {
                    if (bit > 0) {
                        current++;
                    } else {
                        if (current > result) {
                            result = current;
                        }
                        current = 0;
                    }
                }
                if (current > result) {
                    result = current;
                }
            }
        }
        return result;
    }
}

3. Longest Consecutive Sequence Solution JavaScript

var longestConsecutive = function(nums) {
    if(nums.length==0) return 0
    let count=1, max = 1
    nums.sort((a, b) => a - b)
    for(let i=0; i<nums.length; i++) {
        if(nums[i]- nums[i-1] == 1) {
            count=count+1 ;
            max = Math.max(max, count)
        } 
        else if(nums[i]==nums[i-1]) continue
        else {
            count = 1
        }
    }
    return max
};

4. Longest Consecutive Sequence Solution Python

class Solution(object):
    def longestConsecutive(self, nums):
        longest = 0
        num_set = set(nums)
        for n in num_set:
            if (n-1) not in num_set:
                length = 1
                while (n+length) in num_set:
                    length += 1
                longest = max(longest, length)
        return longest