lc128

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

For example,
Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

Your algorithm should run in O(n) complexity.

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        unordered_map<int, int> mp;
        int mx = INT_MIN;
        for (int i:nums) {
            if (!mp[i]) {
                mp[i] = mp[i+1] + mp[i-1] + 1;
                mp[i+mp[i+1]] = mp[i];
                mp[i-mp[i-1]] = mp[i];
                if (mp[i] > mx) mx = mp[i];
            }
        }
        return mx;
    }
};