Set Intersection

Question 3 in the exam
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Sample code

function intersect1(a, b) { //fast
    let s = new Set()
    for (let x of a)
      if (b.has(x)) s.add(x)
    return s
}
function intersect2(a, b) { //slow
    let s = new Set()
    for (let x of a)
      for (let y of b)
        if (x == y) s.add(x)
    return s
}