leetcode. longest contiguous sequence hash table .128

1. Specific topics

To a given integer array unsorted, to find the length of the longest contiguous sequence. The time requirements of the algorithm complexity is O (n).

Example:

Input: [100, 4, 200, 1, 3, 2] Output: 4 explained: the longest contiguous sequence is [1, 2, 3, 4]. Its length is 4.

2. Analysis of ideas

As the title does not require a continuous sequence elements are ordered in the original array, for as long as a number to find out if there are several adjacent to the array, so consider an element into the HashSet achieve  O (1) time query .

3. Code

 1 public int longestConsecutive(int[] nums) {
 2         HashSet set = new HashSet(); 
 3         int longest = 0;
 4         for(int num : nums){
 5             set.add(num);
 6         }
 7         for(int num : nums){ 
 8                 if(set.remove(num)){
 9                 int count = 1;
10                 int current = num;
11                 while(set.remove(--current)) count++;
12                 current = num;
13                 while(set.remove(++current)) count++;
14                 longest = Math.max(longest, count);
15              }
16         }
17         return longest;
18 }