Longest Consecutive Subsequence

gistfile1.txt

/* 
Given an unsorted array of integersarr, return the length of the longest consecutive elements sequence.
 
You must write an algorithm that runs in O(n) time.
 
 
 
Example 1:
 
Input:arr = [100,4,200,1,3,2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
Example 2:
 
Input:arr = [0,3,7,2,5,8,4,6,0,1]
Output: 9
 
 
Constraints:
 
0 <=arr.length <= 105
-109 <=arr[i] <= 109
 
*/

const sortNumbers = (numbers) => {
  for (let i = 0; i < numbers.length - 1; i++) {
    for (let j = i + 1; j < numbers.length; j++) {
      if (numbers[i] > numbers[j]) {
        const tmp = numbers[i];
        numbers[i] = numbers[j];
        numbers[j] = tmp;
      }
    }
  }
};
 
const countLongestConsecutiveSequence = (numbers) => {
    let current = 0;
    let longest = 0;
    
    for (let i = 0; i <= numbers.length; i++) {
      const currentValue = numbers[i];
      const previousValue = numbers[i - 1] + 1;
      
      if (i > 0 && currentValue === previousValue) {
        current++;
      } else {
        current = 1;
      }
      
      longest = Math.max(longest, current);
    }
    
    return longest;
};

const numbers = [
  0, 1, 2, 2, 3, 9, 10, 11, 12, 13, 14, 15, 16, 1, 2, 3, 4, 5, 6, 9, 10, 15, 0,
  17,
];

sortNumbers(numbers);

const result = countLongestConsecutiveSequence(numbers);

console.log(result);