firstDuplicate google

firstDuplicate.ts

function firstDuplicate(a: number[]=[2, 1, 3, 5, 3, 2]): number {


 let set = new Set()
    for (let e of a){
        if (set.has(e))
            return e
        else
            set.add(e)
            }
    return -1


}

console.log(firstDuplicate())