First Missing Positive

HardArraysHashing

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

Practice this as a mock interviewFree to start, no account needed

Problem

Given an unsorted integer array nums, return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space.

Examples

Input: nums = [1,2,0]
Output: 3
Input: nums = [3,4,-1,1]
Output: 2
Input: nums = [7,8,9,11,12]
Output: 1

Constraints

  • 1 <= nums.length <= 10^5
  • -2^31 <= nums[i] <= 2^31 - 1

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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