LeetCode力扣之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.

package leetCode;

import java.util.HashMap;

/**
 * Created by lxw, [email protected] on 2018/3/26.
 */
public class L128_LongestConsecutiveSequence {

    public int longestConsecutive(int[] num){
        int res =0;
        HashMap, Integer> map = new HashMap<>();
        for (int n : num){
            if (!map.containsKey(n)){
                int left = (map.containsKey(n-1)) ? map.get(n-1) : 0;
                int right = (map.containsKey(n+1)) ? map.get(n+1) :0;
                int sum = left + right + 1;
                map.put(n,sum);

                res = Math.max(res, sum);
                map.put(n-left, sum);
                map.put(n+right, sum);
            } else {
                continue;
            }
        }
        return res;
    }
}