LeetCode 128. Longest Consecutive Sequence (javascript solution)

#algorithms #javascript

Description:

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

You must write an algorithm that runs in O(n) time.

Solution:

Time Complexity : O(n)
Space Complexity: O(n)

var longestConsecutive = function(nums) {
    // Handle base case of empty array
    if (!nums.length) return 0;

    // Give ability to look up nums by value
    const set = new Set(nums);
    let max = 0;

    for (const num of set) {
        // Make sure we are starting at the beginning of the sequenece
        if (set.has(num - 1)) continue;

        let currNum = num;
        let currMax = 1;

        // Look numbers that make a consecutive sequence
        while (set.has(currNum + 1)) {
          currNum++;
          currMax++;
        }
        // Update max
        max = Math.max(max, currMax);
    }

    return max;
};