【原创】C++STL multiset

资料来源：官方文档

multiset是一个按照特定排序储存元素的容器，多个元素可以有相同的值。元素的值即为其本身的键值。multiset中的值无法修改，可插入删除。常用于实现二叉树。

定义一个multiset:

 1 // constructing multisets
 2 #include 
 3 #include <set>
 4 using namespace std;
 5 bool fncomp (int lhs, int rhs) {return lhs<rhs;}
 6 
 7 struct classcomp {
 8   bool operator() (const int& lhs, const int& rhs) const
 9   {return lhs<rhs;}
10 };
11 
12 int main ()
13 {
14   multiset<int> first;                          //基本定义
15 
16   int myints[]= {10,20,30,20,20};
17   multiset<int> second (myints,myints+5);       // pointers used as iterators
18 
19   multiset<int> third (second);                 // 复制
20 
21   multiset<int> fourth (second.begin(), second.end());  // iterator ctor.
22 
23   multiset<int,classcomp> fifth;                // class as Compare
24 
25   bool(*fn_pt)(int,int) = fncomp;
26   multiset<int,bool(*)(int,int)> sixth (fn_pt); // function pointer as Compare
27 
28   return 0;
29 }

容器间赋值：

 1 // assignment operator with multisets
 2 #include 
 3 #include <set>
 4 
 5 int main ()
 6 {
 7   int myints[]={ 19,81,36,36,19 };
 8   std::multiset<int> first (myints,myints+5);   // multiset with 5 ints
 9   std::multiset<int> second;                    // empty multiset
10 
11   second=first;                                 // now second contains the 5 ints
12   first=std::multiset<int>();                   // 清空first
13 
14   std::cout << "Size of first: " << first.size() << '\n';
15   std::cout << "Size of second: " << second.size() << '\n';
16   return 0;
17 }

输出为：

1 Size of first: 0
2 Size of second: 5

遍历容器：

int main ()
{
  int myints[] = {42,71,71,71,12};
  multiset<int> mymultiset (myints,myints+5);

  multiset<int>::iterator it;//定义一个在multiset上的iterator

  cout << "mymultiset contains:";
  for (multiset<int>::iterator it=mymultiset.begin(); it!=mymultiset.end(); ++it)
    cout << ' ' << *it;

  cout << '\n';

  return 0;
}

输出：

mymultiset contains: 12 42 71 71 71

插入操作：

 

int main ()
{
  multiset<int> mymultiset;
  multiset<int>::iterator it;

  // set some initial values:
  for (int i=1; i<=5; i++) mymultiset.insert(i*10);  // 10 20 30 40 50

  it=mymultiset.insert(25);

  it=mymultiset.insert (it,27);    // max efficiency inserting
  it=mymultiset.insert (it,29);    // max efficiency inserting
  it=mymultiset.insert (it,24);    // no max efficiency inserting (24<29)

  int myints[]= {5,10,15};
  mymultiset.insert (myints,myints+3);

  cout << "mymultiset contains:";
  for (it=mymultiset.begin(); it!=mymultiset.end(); ++it)
    cout << ' ' << *it;
  cout << '\n';

  return 0;
}

 

输出：

myset contains: 5 10 10 15 20 24 25 27 29 30 40 50

删除某个特定元素：

 1 int main ()
 2 {
 3   std::multiset<int> mymultiset;
 4   std::multiset<int>::iterator it;
 5 
 6   // insert some values:
 7   mymultiset.insert (40);                            // 40
 8   for (int i=1; i<7; i++) mymultiset.insert(i*10);   // 10 20 30 40 40 50 60
 9 
10   it=mymultiset.begin();
11   it++;                                              //    ^
12 
13   mymultiset.erase (it);                             // 10 30 40 40 50 60
14 
15   mymultiset.erase (40);                             // 10 30 50 60
16 
17   it=mymultiset.find (50);
18   mymultiset.erase ( it, mymultiset.end() );         // 10 30
19 
20   cout << "mymultiset contains:";
21   for (it=mymultiset.begin(); it!=mymultiset.end(); ++it)
22    cout << ' ' << *it;
23   cout << '\n';
24 
25   return 0;
26 }

清空容器：

1 multiset<int> list;
2 list.clear();