Leetcode no. 128

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128. Longest Consecutive Sequence

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.

public class Solution {    public int longestConsecutive(int[] nums) {        if (nums.length<=1) return nums.length;            Map<Integer, Integer> map= new HashMap<>();            int res=0;            for (int ele: nums){                if (!map.containsKey(ele)){                    int left= map.containsKey(ele-1)?map.get(ele-1):0;                    int right= map.containsKey(ele+1)?map.get(ele+1):0;                    int sum= left+right+1;                    res=Math.max(res,sum);                    map.put(ele,sum);                    map.put(ele-left,sum);                    map.put(ele+right,sum);                }            }            return res;    }}

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