[구현] Picking Numbers

func pickingNumbers(a: [Int]) -> Int {
    // Write your code here
    let uniqueArr = Array(Set(a))
    var arr = [Int]()
    var res = [Int]()
    var max = 0
    
    for n in uniqueArr {
        for e in a {
            if n - e <= 1, n - e >= 0 {
                arr.append(n-e)
            } 
        }
        if arr.count > max {
            max = arr.count
            res = arr
        }
        arr = []
    }
    
    return res.count
}