Longest Consecutive Sequence

"""
Store all numbers in a hash map for O(1) existence checking.
For each number, only start counting if it is the beginning of a sequence (i-1 is missing).
Then expand forward (i, i+1, i+2...) while numbers exist in the map and track the length.
The maximum length found across all starts is the longest consecutive sequence.

Trick:
When you start checking the longest consecutive elements, check for all the elements of the map because array can have a lot of the duplicates.
"""

class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        dict={}
        for i in nums:
            dict[i]=dict.get(i,0)+1
        ans=0
        for i in dict.keys():
            ele=i
            if dict.get(ele-1,0)==0:
                cur=0
                while dict.get(ele,0)!=0:
                    cur+=1
                    ele+=1
                if cur>ans:
                    ans=cur
        return ans