Fresher · Arrays & hashing

Remove Duplicate Values

Return the unique numbers from an array in their original order. Do not mutate the input.

Examples

[1, 2, 1, 3, 2] → [1, 2, 3]

Linear search

Repeated membership scans are simple but can be quadratic.

Time: O(n²) · Space: O(n)

function unique(nums) {
  const result = [];
  for (const n of nums) if (!result.includes(n)) result.push(n);
  return result;
}

Set

Set preserves insertion order and has expected constant-time insertion.

Time: O(n) expected · Space: O(n)

function unique(nums) {
  return [...new Set(nums)];
}