function findMissing(arr1, arr2) { let str = arr1.filter(i => !arr2.includes(i)).join(''); return Number(str); } Test.assertEquals(findMissing([1, 2, 3], [1, 3]), 2); Test.assertEquals(findMissing([6, 1, 3, 6, 8, 2], [3, 6, 6, 1, 2]), 8); Test.assertEquals(findMissing([7], []), 7);