Longest Consecutive Sequence

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.

 1 public class Solution {
 2     public int longestConsecutive(int[] num) {
 3         int len = num.length;
 4         HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
 5         boolean [] visited =new boolean[len];
 6         for(int i=0;i<len;i++){
 7             hm.put(num[i],i);
 8         }
 9         int res = 0;
10         for(int i=0;i<len;i++){
11             int count = 1;
12             if(visited[i]) continue;
13             int index = num[i];
14             while(hm.containsKey(--index)){
15                 count++;
16                 visited[hm.get(index)]=true;
17             }
18             index = num[i];
19             while(hm.containsKey(++index)){
20                 count++;
21                 visited[hm.get(index)]=true;
22             }
23             res = Math.max(count,res);
24         }
25         return res;
26     }
27 }
View Code

 visited[hm.get(n)] = true;

posted @ 2014-02-06 15:03  krunning  阅读(251)  评论(0)  编辑  收藏  举报