题目
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.

答案

class Solution {
    public int longestConsecutive(int[] nums) {
        if(nums.length == 0) return 0;
        int max = 1;
        HashSet<Integer> set = new HashSet<Integer>();
        for(int num : nums) set.add(num);
        for(int sample : nums) {
            if(!set.contains(sample)) continue;
            int left = sample , right = sample;
            while(set.contains(--left)) set.remove(left);
            while(set.contains(++right)) set.remove(right);
            max = Math.max((right - 1) - (left + 1) + 1, max);
        }
        return max;
    }
}