Question d’entretien chez Dekoruma

Given array of integers. Find the smallest positive integer number greater than 0 that missing from that array. Example : [-1, 6, 1, 10, 2, 5, -2, 11] return 3 [1,0,-19,21,3,4,-2] return 2 [1,1,2] return 3 [] return 1 [15] return 1 [1,2,4] return 3