### Problem

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

#### Example

Given [100, 4, 200, 1, 3, 2], the longest consecutive elements sequence should be [1, 2, 3, 4]. Its length is 4.

The algorithm should run in O(n) complexity.

### JavaScript Code

function longestConsecutive(num) { // if array is empty, return 0 if (num.length == 0) { return 0; } var set = []; var max = 1; for (var i=0; i<num.length; i++) set.push(num[i]); for (var i=0; i<num.length; i++) { var left = num[i] - 1; var right = num[i] + 1; var count = 1; while (set.indexOf(left) != -1) { count++; set.splice(set.indexOf(left), 1); left--; } while (set.indexOf(right) != -1) { count++; set.splice(set.indexOf(right), 1); right++; } max = Math.max(count, max); } return max; } console.log(longestConsecutive([4,3,2,0,8]));

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