This is a demo task. Write a function: class Solution { public int solution(int[] A); } that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A. For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5. Given A = [1, 2, 3], the function should return 4. Given A = [1, 3], the function should return 1. Write an efficient algorithm for the following assumptions: N is an integer within the range [1..100,000]; each element of array A is an integer within the range [1,000,000..1,000,000].

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