集合的另一种实现方式

type IntSet struct {
	words []int64
}

/*集合是否包含某个元素*/
func (s *IntSet) Has(x int) bool {
	word, bit := x/64, uint(x%64)
	return word < len(s.words) && s.words[word]&(1<<bit) != 0
}

/*向集合中添加元素*/
func (s *IntSet) Add(x int) {
	word, bit := x/64, uint(x%64)
	for word >= len(s.words) {
		s.words = append(s.words, 0)
	}
	s.words[word] |= 1 << bit
}

/*集合的并集操作*/
func (s *IntSet) UnionWith(t *IntSet) {
	for i, tword := range t.words {
		if i < len(s.words) {
			s.words[i] |= tword
		} else {
			append(s.words, tword)
		}
	}
}

/*集合的交集操作*/
func (s *IntSet) Intersection(t *IntSet) *IntSet {
	dest := new(IntSet)
	for i, tword := range t.words {
		if i < len(s.words) {
			for j := 0; j < 64; j++ {
				bitvalue := int64(1 << uint(j))
				if (tword&bitvalue != 0) && (s.words[i]&bitvalue != 0) {
					for k := len(dest.words) - 1; k <= i; k++ {
						dest.words = append(dest.words, 0)
					}
					dest.words[i] |= bitvalue
				}
			}
		}	
	}
	return dest
}
/*集合的字符串转换*/
func (s *IntSet) String() string {
	var buf bytes.Buffer
	buf.WriteByte('{')
	for i, word := range s.words {
		if word == 0 {
			continue
		}

		for j := 0; j < 64; j++ {
			if word&(1<<uint(j)) != 0 {
				if buf.Len() > len("{") {
					buf.WriteByte(' ')
				}
				fmt.Fprintf(&buf, "%d", 64*i + j)
			}
		}
	}
	buf.WriteByte('}')
	return buf.String()
}

func main() {
	var x, y IntSet
	x.Add(1)
	x.Add(144)
	x.Add(9)
	fmt.Println(x.String())

	y.Add(9)
	y.Add(32)
	fmt.Println(x.String())

	fmt.Println((x.Intersection(y)).String()) /*{9}*/
}