题目要求：

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.

题目地址：https://leetcode.com/problems/longest-consecutive-sequence/

public class Solution {        public static int longestConsecutive(int[] num) {        HashMap
     
       hash_array=new HashMap 
      
       ();        for(int ele: num){            hash_array.put(new Integer(ele), new Boolean(false));                  }        int max_result=0;        for(int element:num){            int result=0;                        for(int ele_x=element;(hash_array.containsKey(ele_x))                     && (hash_array.get(ele_x)==false);ele_x++){                hash_array.put(new Integer(ele_x),new Boolean(true));                result++;            }            for(int ele_y=element-1;hash_array.containsKey(ele_y)                    &&(hash_array.get(ele_y)==false);ele_y--){                hash_array.put(new Integer(ele_y),new Boolean(true));                result++;            }            max_result=result>max_result?result:max_result;                              }        return max_result;    }｝
      
     

数据结构题型，主要复杂度是N不能先排序在遍历最长连续子串，考虑使用hash表查找，查找复杂度就变成了1，把所有元素遍历完一遍后，即能得出最长连续子串。