Find the Smallest Missing Positive Number in an Array O(n)

 1// findSmallestMissingNumber finds the smallest missing positive integer in the array
 2func findSmallestMissingNumber(nums []int) int {
 3    n := len(nums)
 4
 5    // Traverse the array, placing each number in its correct position
 6    for i := 0; i < n; i++ {
 7        for nums[i] > 0 && nums[i] <= n && nums[nums[i]-1] != nums[i] {
 8            nums[i], nums[nums[i]-1] = nums[nums[i]-1], nums[i]
 9        }
10    }
11
12    // Traverse the array again to find the first number not in its correct position
13    for i := 0; i < n; i++ {
14        if nums[i] != i + 1 {
15            return i + 1
16        }
17    }
18
19    // If the array contains numbers from 1 to n, the smallest missing number is n+1
20    return n + 1
21}