题目：

题解：

type PeekingIterator struct {
    iter     *Iterator
    _hasNext bool
    _next    int
}

func Constructor(iter *Iterator) *PeekingIterator {
    return &PeekingIterator{iter, iter.hasNext(), iter.next()}
}

func (it *PeekingIterator) hasNext() bool {
    return it._hasNext
}

func (it *PeekingIterator) next() int {
    ret := it._next
    it._hasNext = it.iter.hasNext()
    if it._hasNext {
        it._next = it.iter.next()
    }
    return ret
}

func (it *PeekingIterator) peek() int {
    return it._next
}