In this post, we are going to solve the Longest Consecutive Sequence Leetcode Solution problem of Leetcode. This Leetcode problem is done in many programming languages like C++, Java, and Python.

Problem
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
Now, let’s see the leetcode solution of Longest Consecutive Sequence Leetcode Solution.
Longest Consecutive Sequence Leetcode Solution in Python
class Solution: def longestConsecutive(self, nums: List[int]) -> int: ans = 0 seen = set(nums) for num in nums: if num - 1 in seen: continue length = 0 while num in seen: num += 1 length += 1 ans = max(ans, length) return ans
Longest Consecutive Sequence Leetcode Solution in CPP
class Solution { public: int longestConsecutive(vector<int>& nums) { int ans = 0; unordered_set<int> seen{begin(nums), end(nums)}; for (int num : nums) { // Num is the start of a sequence if (seen.count(num - 1)) continue; int length = 1; while (seen.count(++num)) ++length; ans = max(ans, length); } return ans; } };
Longest Consecutive Sequence Leetcode Solution in Java
class Solution { public int longestConsecutive(int[] nums) { int ans = 0; Set<Integer> seen = Arrays.stream(nums).boxed().collect(Collectors.toSet()); for (int num : nums) { // Num is the start of a sequence if (seen.contains(num - 1)) continue; int length = 1; while (seen.contains(++num)) ++length; ans = Math.max(ans, length); } return ans; } }
Note: This problem Longest Consecutive Sequence is generated by Leetcode but the solution is provided by Chase2learn This tutorial is only for Educational and Learning purpose.