LeetCode - 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.

采用两个HashMap，一个存放在序列最小值，及其对应的长度。另一个存放序列最大值，及其对应的长度，要注意的时候，对这两个map中值的更新操作。

public class Solution {
    public int longestConsecutive(int[] num) {
        // Start typing your Java solution below
        // DO NOT write main() function
        Map<Integer, Integer> big = new HashMap<Integer, Integer>();
        Map<Integer, Integer> small = new HashMap<Integer, Integer>();
        int max = 1;
        for (int i=0; i<num.length; i++) {
            int value = num[i];
            if (big.get(value)!=null || small.get(value)!=null)
                continue;
            
            if (big.get(value-1)!=null && small.get(value+1)!=null) {
                big.put(value, 1);
                int l1 = big.get(value-1);
                int l2 = small.get(value+1);
                int length = l1+l2+1;
                big.put(value+l2, length);
                small.put(value-l1, length);
                max = Math.max(max, length);
            } else if (big.get(value-1) != null) {
                int length = big.get(value-1)+1;
                big.put(value, length);
                small.put(value-length+1, length);
                max = Math.max(max, length);
            } else if (small.get(value+1) != null) {
                int length = small.get(value+1)+1;
                small.put(value, length);
                big.put(value+length-1, length);               
                max = Math.max(max, length);
            } else {
                big.put(value, 1);
                small.put(value, 1);
            }
                
        }
        
        return max;
    }
}