【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:

// constructing multisets
#include <iostream>
#include <set>
using namespace std;
bool fncomp (int lhs, int rhs) {return lhs<rhs;}

struct classcomp {
  bool operator() (const int& lhs, const int& rhs) const
  {return lhs<rhs;}
};

int main ()
{
  multiset<int> first;                          //基本定义

  int myints[]= {10,20,30,20,20};
  multiset<int> second (myints,myints+5);       // pointers used as iterators

  multiset<int> third (second);                 // 复制

  multiset<int> fourth (second.begin(), second.end());  // iterator ctor.

  multiset<int,classcomp> fifth;                // class as Compare

  bool(*fn_pt)(int,int) = fncomp;
  multiset<int,bool(*)(int,int)> sixth (fn_pt); // function pointer as Compare

  return 0;
}

容器间赋值：

// assignment operator with multisets
#include <iostream>
#include <set>

int main ()
{
  int myints[]={ 19,81,36,36,19 };
  std::multiset<int> first (myints,myints+5);   // multiset with 5 ints
  std::multiset<int> second;                    // empty multiset

  second=first;                                 // now second contains the 5 ints
  first=std::multiset<int>();                   // 清空first

  std::cout << "Size of first: " << first.size() << '
';
  std::cout << "Size of second: " << second.size() << '
';
  return 0;
}

输出为：

Size of first: 0
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 << '
';

  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 << '
';

  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：

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

  // insert some values:
  mymultiset.insert (40);                            // 40
  for (int i=1; i<7; i++) mymultiset.insert(i*10);   // 10 20 30 40 40 50 60

  it=mymultiset.begin();
  it++;                                              //    ^

  mymultiset.erase (it);                             // 10 30 40 40 50 60

  mymultiset.erase (40);                             // 10 30 50 60

  it=mymultiset.find (50);
  mymultiset.erase ( it, mymultiset.end() );         // 10 30

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

  return 0;
}

清空容器：

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