First Missing Positive

Return the smallest positive integer absent from an unsorted array in O(n) time and O(1) extra space. First Missing Positive Return the smallest positive integer absent from an unsorted array in O(n) time and O(1) extra space. SWE array hard Frequency Single report Last asked 2026-03-11 Stage phone-screen · onsite-coding First Missing Positive Given an unsorted integer array nums, return the smallest positive integer that does not appear in nums. Your solution must run in O(n) time and use O(1) extra space. Examples Example 1: Input: nums = [1,2,0] Output: 3 Explanation: The values 1 and 2 are present, so the smallest missing positive is 3. Example 2: Input: nums = [3,4,-1,1] Output: 2 Example 3: Input: nums = [7,8,9,11,12] Output: 1 Constraints 1 <= nums.length <= 10^5 -2^31 <= nums[i] <= 2^31 - 1