[leedcode 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) {
        //考虑到可能存在重复元素，本题借助set数据结构，遍历set中每一个数字，
        //然后从前后两个方向进行寻找，遍历过程保存长度值，同时删除已经遍历的元素
        Set<Integer> set=new HashSet<Integer>();
        for(int i=0;i<nums.length;i++){
            set.add(nums[i]);
        }

        int res=0;
        for(int i=0;i<nums.length;i++){
            if(set.contains(nums[i])){
                int len=1;
                int left=nums[i]-1;
                int right=nums[i]+1;
                set.remove(nums[i]);
                while(set.contains(left)){
                    set.remove(left);
                    left--;
                    len++;

                }
                while(set.contains(right)){
                    set.remove(right);
                    right++;
                    len++;
                }
                if(len>res)res=len;
            }
        }
        return res;
    }
}