[Leetcode] 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.

Ideas:

Use set to store the different elements in the array first. The elements within the set are then searched sequentially, as follows:

1. Read the header element A in the collection and remove it from the collection;

2. Find the value of A+1 in the collection (Set.contains () method), if any, delete the element, continue to find a+2...a+m,a+m+1 does not exist, then jump out of the loop;

3. Find the value of A-1 in the collection exists, if there is an element, continue to find a-2...a-p,a-p-1 does not exist, then jump out of the loop;

4. The value of the record m+p+1 is the longest sequential number found, comparing it with Max and selecting the maximum;

5. Select the head element again, repeating the process until the collection element is traversed.

Code: (Java)

1  Public classSolution {2      Public intLongestconsecutive (int[] nums) {3         if(nums.length==1){4             return1;5         }6Set<integer> Arrset =NewHashset<integer>();7          for(inti=0;i<nums.length;i++){8 Arrset.add (Nums[i]);9         }TenIterator<integer> iter =arrset.iterator (); One         intMax = 0; A          while(Iter.hasnext ()) { -             intCount1=0; -             intCount2=0; the             intA = Iter.next () +1; -             intb = a-2; - Iter.remove (); -Iterator<integer> it1 =arrset.iterator (); +             if(It1.hasnext ()) { -                  while(It1.hasnext () && arrset.contains (a++)){ +count1++; AArrset.remove (A-1); at                 } -             } -Iterator<integer> it2 =arrset.iterator (); -             if(It2.hasnext ()) { -                  while(It2.hasnext () && arrset.contains (b--)){ -count2++; inArrset.remove (b+1); -                 } to             } +max = Math.max (max,count1+count2+1); -ITER =arrset.iterator (); the         } *         returnMax; $     }Panax Notoginseng}

[Leetcode] Longest consecutive Sequence