*[Lintcode]Longest Consecutive Sequence最长连续序列

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Example

Given [100, 4, 200, 1, 3, 2],
The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.

分析：O(n)复杂度的话，不可以使用排序。所以空间换时间。将数组存入List。每次取一个值，找相邻的值并remove，直到没有相邻的值。

public class Solution {
    /**
     * @param nums: A list of integers
     * @return an integer
     */
    public int longestConsecutive(int[] num) {
        if(num.length == 0) return 0;
        List<Integer> res = new ArrayList<Integer>();
        
        for(int i = 0; i < num.length; i++) {
            res.add(num[i]);
        }
        
        int max = 1;
        for(int i = 0; i < num.length; i++) {
            int key = num[i];
            if(res.contains(key)) {
                int tmp = 1;
                res.remove(res.indexOf(key));
                if(res.contains(key + 1) || res.contains(key - 1)) {
                    int newKey = key;
                    while(res.contains(newKey + 1)) {
                        tmp ++;
                        res.remove(res.indexOf(newKey + 1));
                        newKey += 1;
                    }
                    newKey = key;
                    while(res.contains(newKey - 1)) {
                        tmp ++;
                        res.remove(res.indexOf(newKey - 1));
                        newKey -= 1;
                    }
                }
                max = Math.max(max, tmp);
            }
        }      
        return max;
    }
}