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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<Integer,Boolean> hash_array=new HashMap <Integer,Boolean>(); 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。
leetcode:Longest Consecutive Sequence
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原文地址：http://www.cnblogs.com/charlesdoit/p/4331021.html
