LeetCode-128. Longest Consecutive Sequence [C++][Java]

LeetCode-128. Longest Consecutive Sequencehttps://leetcode.com/problems/longest-consecutive-sequence/

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 <= 10^5
• -10^9 <= nums[i] <= 10^9

class Solution {
public:
    int longestConsecutive(vector& nums) {
        unordered_set hash;
        for (const int & num: nums) {
            hash.insert(num);
        }
        int ans = 0;
        while (!hash.empty()) {
            int cur = *(hash.begin());
            hash.erase(cur);
            int next = cur + 1, prev = cur - 1;
            while (hash.count(next)){
                hash.erase(next++);
            }
            while (hash.count(prev)) {
                hash.erase(prev--);
            }
            ans = max(ans, next - prev - 1);
        }
        return ans;
    }
};

class Solution {
    public int longestConsecutive(int[] nums) {
        HashSet set=new HashSet();
        int maxLen  =0;
        for(int k :nums){
            set.add(k);
        }
        for(int i=0; i