leetcode学习笔记56

128. Longest Consecutive Sequence

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

Your algorithm should run in O(n) complexity.

Example:

Input: [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

class Solution {
    public int longestConsecutive(int[] nums) {
        if(nums.length==0)return 0;
        Set<Integer> set=new TreeSet<Integer>();
        for(int num:nums){
            set.add(num);
        }
        int pre=Integer.MIN_VALUE,count=1,res=1;
        for(int num:set){
            if(num-pre==1){
                count++;
                if(count>res){
                    res=count;
                }
            }else{
                count=1;
            }
            pre=num；
        }
        return res;
    }
}