func (s *IntSync) Contains(num int) bool {
	s.RLock()
	defer s.RUnlock()
	_, ok := s.nodeMap[num]
	return ok
}
Contains - Check if item exists in set
package set
import "sync"
type IntSync struct {
	nodeMap map[int]struct{}
	sync.RWMutex
}
func NewIntSync(nums []int) *IntSync {
	s := &IntSync{}
	for _, num := range nums {
		s.Add(num)
	}
	return s
}
func (s *IntSync) Add(num int) *IntSync {
	s.Lock()
	defer s.Unlock()
	if s.nodeMap == nil {
		s.nodeMap = make(map[int]struct{})
	}
	_, ok := s.nodeMap[num]
	if !ok {
		s.nodeMap[num] = struct{}{}
	}
	return s
}
func (s *IntSync) Clear() {
	s.Lock()
	defer s.Unlock()
	s.nodeMap = make(map[int]struct{})
}
func (s *IntSync) Remove(num int) bool {
	s.Lock()
	defer s.Unlock()
	_, ok := s.nodeMap[num]
	if ok {
		delete(s.nodeMap, num)
	}
	return ok
}