[Leetcode] [Java] Longest consecutive Sequence

Title:

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.

Test Instructions:

Returns the length of the longest contiguous element given an unordered array of integers.

Given [100, 4, 200, 1, 3, 2] ,

The longest sequential sequence of elements is [1, 2, 3, 4]. The length returned is: 4.

The complexity of your algorithm should be O (n).

Algorithm Analysis:

* Sort words to at least O (nlgn) complexity.

* O (n) complexity, currently only found using hash to solve the scheme,

* Add, remove, contains, etc. the complexity of the method is O (1), so the operating complexity of the two traversal is O (n).

* First put the number in a set, get a number, go to the side of the search, get the longest string containing this number,

* and remove the used number from the set (because of a continuous relationship, a number does not appear in two strings). The last comparison is whether the current string is longer than the current maximum string and is updated.

* Continue so until the collection is empty.

* After a element is checked, it should was removed from the set.

* Otherwise, time complexity would be O (MN) in which m are the average length of all consecutive sequences.

AC Code:

<span style= "FONT-SIZE:12PX;" >public static int longestconsecutive (int[] num)     {    //If array is empty, return 0    if (num.length = = 0)     return 0;        set<integer> set = new Hashset<integer> ();    int max = 1;         for (int e:num)    set.add (e);         for (int e:num)     {    int left = e-1;    int right = e + 1;    int count = 1;         while (Set.contains (left))     {    count++;    Set.remove (left);    left--;    }         while (Set.contains (right))     {    count++;    Set.remove (right);    right++;    }         max = Math.max (count, max);    }    return max;}    } </span>

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[Leetcode] [Java] Longest consecutive Sequence