Array Manipulation with Strict Limits | Dataford Interview Questions

Solve a medium-to-hard array manipulation problem under strict time and space complexity requirements.

Implement first_missing_positive(nums) to return the smallest positive integer absent from the input array. The algorithm must run in O(n) time and use O(1) extra space, excluding the input array. The function may modify nums in place.

I/O Contract

Input: an array of integers nums.
Output: one integer representing the smallest missing positive value.

Constraints

1 <= nums.length <= 100000
-2147483648 <= nums[i] <= 2147483647
The function may modify nums in place
Use O(n) time and O(1) extra space

Function Signature

def first_missing_positive(nums):

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