STL --> set用法

1、set和multiset基础

set和multiset会根据特定的排序准则，自动将元素进行排序。不同的是后者允许元素重复而前者不允许。

需要包含头文件：

#include <set>

2、创建元素

set<int> s1;    　　　　　　　　　　　　　　　　//创建空的set对象，元素类型为int，
set<const char*, strLess> s2( strLess);     //创建空的set对象，元素类型char*，比较函数对象(即排序准则)为自定义strLess
set<int> s3(s1);    　　　　　　　　　　　　　　//利用set对象s1,拷贝生成set对象s2
int iArray[] = {13, 32, 19};
set<int> s4(iArray, iArray + 3);    　　　　　//用迭代区间[&first, &last)所指的元素，创建一个set对象
const char* szArray[] = {"hello", "dog", "bird" };
set<const char*, strLess> s5(szArray, szArray + 3, strLess() );    //用迭代区间[&first, &last)所指的元素，及比较函数对象strLess，创建一个set对象

3、插入元素

set<string> set1;    //empty set
set1.insert("the");   //set1 now has one element
set1.insert("and");   //set1 now has two elements
set<int> set2;    //empty set
set2.insert(iset.begin(), iset.end());       //set2 now has 10 elements

例如：

// set::insert (C++98)
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  std::set<int>::iterator it;
  std::pair<std::set<int>::iterator,bool> ret;

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

  ret = myset.insert(20);               // no new element inserted

  if (ret.second==false) it=ret.first;  // "it" now points to element 20

  myset.insert (it,25);                 // max efficiency inserting
  myset.insert (it,24);                 // max efficiency inserting
  myset.insert (it,26);                 // no max efficiency inserting

  int myints[]= {5,10,15};              // 10 already in set, not inserted
  myset.insert (myints,myints+3);

  std::cout << "myset contains:";
  for (it=myset.begin(); it!=myset.end(); ++it)
    std::cout << ‘ ‘ << *it;
  std::cout << ‘\n‘;

  return 0;
}

结果：

myset contains: 5 10 15 20 24 25 26 30 40 50

4、删除元素

// erasing from set
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  std::set<int>::iterator it;

  // insert some values:
  for (int i=1; i<10; i++) myset.insert(i*10);  // 10 20 30 40 50 60 70 80 90

  it = myset.begin();
  ++it;                                         // "it" points now to 20

  myset.erase (it);
  myset.erase (40);

  it = myset.find (60);
  myset.erase (it, myset.end());

  std::cout << "myset contains:";
  for (it=myset.begin(); it!=myset.end(); ++it)
    std::cout << ‘ ‘ << *it;
  std::cout << ‘\n‘;

  return 0;
}

结果：

myset contains: 10 30 50

5、查找元素

iset.find(1);     //returns iterator that refers to the element with key==1
iset.find(11);   //returns iterator == iset.end()
iset.count(1);  //returns 1;
iset.count(11); //returns 0;

//set_it refers to the element with key==1
set<int>::iterator set_it = iset.find(1);
*set_it=11;         //error: keys in a set are read-only
cout<<*set_it<<endl; //ok: can read the key

例如：

// set::find
#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  std::set<int>::iterator it;

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

  it=myset.find(20);
  myset.erase (it);
  myset.erase (myset.find(40));

  std::cout << "myset contains:";
  for (it=myset.begin(); it!=myset.end(); ++it)
    std::cout << ‘ ‘ << *it;
  std::cout << ‘\n‘;

  return 0;
}

结果：

myset contains: 10 30 50

6、其他

    #include <iostream>
    #include <set>
    using namespace std;  

    int main()
    {
        typedef set<int,greater<int> > IntSet;
        IntSet s1;  

        s1.insert(4);
        s1.insert(3);
        s1.insert(5);
        s1.insert(1);
        s1.insert(6);
        s1.insert(2);
        s1.insert(5);
        //the inserted element that has the same value with a element existed is emitted  

        copy(s1.begin(),s1.end(),ostream_iterator<int>(cout," "));
        cout << endl << endl;  

        pair<IntSet::iterator,bool> status = s1.insert(4);
        if(status.second)
            cout << "4 is inserted as element "
            << distance(s1.begin(),status.first) + 1 << endl;
        else
            cout << "4 already exists in s1" << endl;
        copy(s1.begin(),s1.end(),ostream_iterator<int>(cout," "));
        cout << endl << endl;  

        set<int>  s2(s1.begin(),s1.end());//default sort criterion is less<
        copy(s2.begin(),s2.end(),ostream_iterator<int>(cout," "));
        cout << endl << endl;
    }  

上述程序最后新产生一个set：s2，默认排序准则是less。以s1的元素作为初值。

注意：s1和s2有不同的排序准则，所以他们的型别不同，不能直接进行相互赋值或比较。

运行结果：

6 5 4 3 2 1 

4 already exist in s1
6 5 4 3 2 1 

1 2 3 4 5 6