First Missing Positive

 

int firstMissingPositive(int A[], int n) {
    for(int i=0;i<n;i++)
    {
        if(A[i]>0&&A[i]<=n)
        {
            if(A[i]-1!=i&&A[A[i]-1]!=A[i])
            {
                int tmp = A[A[i]-1];
                A[A[i]-1] = A[i];
                A[i] = tmp;
                i--;
            }
        }
    }
    
    for(int i=0;i<n;i++)
        if(A[i]-1!=i)
            return i+1;
    return n+1;
}