练习6.1: 为bit数组实现下面这些方法
func (*IntSet) Len() int // return the number of elements
func (*IntSet) Remove(x int) // remove x from the set
func (*IntSet) Clear() // remove all elements from the set
func (*IntSet) Copy() *IntSet // return a copy of the set
package main import ( "bytes" "fmt" ) func main() { var x, y IntSet x.Add(1) x.Add(144) x.Add(9) fmt.Println(x.String()) // "{1 9 144}" y.Add(9) y.Add(42) fmt.Println(y.String()) // "{9 42}" x.UnionWith(&y) fmt.Println(x.String()) // "{1 9 42 144}" fmt.Println(x.Len()) // 返回4 //x.Remove(9) //"{1 42 144}" z := x.Copy() x.Clear() fmt.Println(x.String()) //返回{} fmt.Println(z.String()) //"{1 9 42 144}" fmt.Println(x.Has(9), x.Has(123)) // "true false" } // An IntSet is a set of small non-negative integers. // Its zero value represents the empty set. type IntSet struct { words []uint64 } // Has reports whether the set contains the non-negative value x. 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 } // UnionWith sets s to the union of s and t. func (s *IntSet) UnionWith(t *IntSet) { for i, tword := range t.words { if i < len(s.words) { s.words[i] |= tword } else { s.words = append(s.words, tword) } } } // String returns the set as a string of the form "{1 2 3}". 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() } /* 练习6.1: 为bit数组实现下面这些方法 */ func (s *IntSet) Len() int { sum := 0 for _, word := range s.words { for j := 0; j < 64; j++ { if word&(1<<uint(j)) != 0 { sum++ } } } return sum } //往集合中添加元素 //1. 或|;两个值其中之一为1,结果为1 //2. 1 << bit 1左移到指定位 //3. a |= b ==> a= a|b 最终实现设置指定位为1 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 } //删除集合中的元素 //1.异或^ :两个值相同,结果为0;两个值不同结果为1; //2.与&:两个值都是1,结果为1;其他结果为0 //3. s.words[word] ^ (1 << bit) 把我指定位的1改成了0 //4. a &= b ==> a=a&b 最终实现设置指定位为0 func (s *IntSet) Remove(x int) { word, bit := x/64, uint(x%64) s.words[word] &= s.words[word] ^ (1 << bit) } //清空集合 //1. 设置每个位都为0 //2. 使用异或,把位是1的改成0 func (s *IntSet) Clear() { for i, word := range s.words { for j := 0; j < 64; j++ { if word&(1<<uint(j)) != 0 { s.words[i] ^= 1 << uint(j) } } } } //copy一个set //编译器判断变量的生命期会超出作用域后,自动在堆上分配 func (s *IntSet) Copy() (r *IntSet) { var result IntSet for _, word := range s.words { result.words = append(result.words, word) } return &result }