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;    }}