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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.
答案
public class Solution { public int longestConsecutive(int[] num) { if(num==null||num.length==0) { return 0; } int result=1; HashSet<Integer> set=new HashSet<Integer>(); Map<Integer,Integer>map=new HashMap<Integer,Integer>(); for(int element:num) { set.add(element); } for(int element:num) { if(map.containsKey(element)) { continue; } int end=element; for(end=element+1;set.contains(end)&&!map.containsKey(end);end++); int len=end-element; if(map.containsKey(end)) { len+=map.get(end); } result=Math.max(len,result); for(int i=element;i<end;i++,len--) { map.put(i,len); } } return result; } }
Longest Consecutive Sequence
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