Before push into stack the conditon should be stack is not empty and top elements of stack bigger than elements before pushing then push the elements into stack

func push(value: Int) {
    while !stack.isEmpty && stack.last > value {
        stack.removeLast()
    }
    stack.append(value)
}
    

Before push into stack the conditon should be stack is not empty and top elements of stack smaller elements before pushing then push the elements into stack

func push(value: Int) {

    while !stack.isEmpty && stack.last < value {
        stack.removeLast()
    }
    stack.append(value)
}