Array Extension #2
mutating func switchValue(_ index1:Int,index2:Int){
    let _index1:Int = (index1 < 0) ? self.count + index1 : index1
    let _index2:Int = (index2 < 0) ? self.count + index2 : index2
    let elm = self[_index1]
    self[_index1] = self[_index2]
    self[_index2] = elm
}