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First Missing Positive (hard)
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Problem Statement

Given an unsorted array nums containing positive and negative integers, return the smallest missing positive integer value.

Note: You must implement algorithm in o(n) time and uses o(1) space.

Examples

  • Example 1:

    • Input: [5, 3, -1, 8, 4, 2]
    • Expected Output: 1
    • Justification: The first missing positive integer in the array is 1.

  • Example 2:

    • Input: [2, 5, -7, 3, 9, 4, 6, 1]
    • Expected Output: 7
    • Justification: The array contains all integers from 1 to 6, so the first missing positive integer is 7.

  • Example 3:

    • Input: [-4, -3, -2, -1]
    • Expected Output: 1
    • Justification: Since there are no positive integers, the first missing positive integer is 1.

Try it yourself

Try solving this question here:

Python3
Python3
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