关于set的用法

男娘i 2022-06-14 00:22 289阅读 0赞

map的元素都是“实值/键值”所形成的一个对组。每个元素都有一个键，是排序的准则。每个键只能出现一次，不允许重复使用。map可以被视为关联式数组，也就是具有任意索引型别的数组。  
set内部的元素根据其值自动排序，可以将set视作一种特殊的map，其元素实值就是键值。

**关于STL中set的用法：**

1、set的迭代器的使用：  
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#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        int arr[] = { 75, 23, 65, 42, 13 };
        set<int>myset(arr, arr + 5);
        set<int>::iterator it1 = myset.begin();//正向迭代器的使用
        while (it1 != myset.end())
        {
            cout << *it1 << " ";
            it1++;
        }
        cout << endl;
        set<int>::reverse_iterator it2 = myset.rbegin();//反向迭代器的使用
        while (it2 != myset.rend())
        {
            cout << *it2 << " ";
            it2++;
        }
        system("pause");
        return 0;
    }

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2、关于set容量的使用方法  
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#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset;
        cout << "empty:"<<myset.empty() << endl;
        cout << "size:"<<myset.size() << endl;
        for (int i = 0; i < 5; i++)
        {
            myset.insert(i);
        }
        cout << "size:" << myset.size() << endl;
        myset.insert(6);
        cout << "size:" << myset.size() << endl;
        cout << "empty:" << myset.empty() << endl;
        system("pause");
        return 0;
    }

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3、关于set的修改操作  
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3.1关于插入操作  
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#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset;
        set<int>::iterator it;
        pair<set<int>::iterator, bool> ret;//如果插入失败则会返回一个pair类型的结构体
        //pair结构体有两个成员在这里定义的第一个成员则是一个set的迭代器类型，第二个成员是一个bool类型
        for (int i = 0; i < 5; i++)
        {
            myset.insert(i * 10);
        }
        ret=myset.insert(20);
        if (ret.second == false)
        {
            it = ret.first;//如果插入失败了，此时set类型的迭代器指向当前插入失败的位置
            cout <<"插入失败" <<*it << endl;
        }
        myset.insert(50);
        myset.insert(60);
        myset.insert(70);
        int arr[] = { 15, 16, 17, 18 };
        myset.insert(arr, arr + 4);//这种方式是按照一段区间直接插入
        it = myset.begin();
        while (it != myset.end())
        {
            cout << *it << " ";
            ++it;
        }
        system("pause");
        return 0;
    }

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3.2、关于删除操作  
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#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset;
        set<int>::iterator it;
        for (int i = 0; i < 5; i++)
        {
            myset.insert(i * 10);
        }   
        myset.erase(0);
        it = myset.begin();
        ++it;
        myset.erase(it);
        it = myset.find(30);
        myset.erase(it,myset.end());
        it = myset.begin();
        while (it != myset.end())
        {
            cout << *it << " ";
            ++it;
        }
        system("pause");
        return 0;
    }

![这里写图片描述][SouthEast 8]

3.3交换操作  
![这里写图片描述][SouthEast 9]

#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset1;
        set<int>::iterator it1;
        for (int i = 0; i < 5; i++)
        {
            myset1.insert(i * 10);
        }   
        set<int>myset2;
        set<int>::iterator it2;
        for (int i = 5; i < 10; i++)
        {
            myset2.insert(i * 10);
        }
        myset1.swap(myset2);
        it1 = myset1.begin();
        cout << "myset1:";
        while (it1 != myset1.end())
        {
            cout << *it1 << " ";
            ++it1;
        }
        cout << endl;
        it2 = myset2.begin();
        cout << "myset2:";
        while (it2 != myset2.end())
        {
            cout << *it2 << " ";
            ++it2;
        }
        system("pause");
        return 0;
    }

![这里写图片描述][SouthEast 10]

3.4清除操作  
![这里写图片描述][SouthEast 11]

#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset1;
        set<int>::iterator it1;
        for (int i = 0; i < 5; i++)
        {
            myset1.insert(i * 10);
        }   
        myset1.clear();
        cout << "myset1:";
        cout << "size:"<<myset1.size() << endl;
        it1 = myset1.begin();
        while (it1 != myset1.end())
        {
            cout << *it1 << " ";
            ++it1;
        }
        cout << endl;
        system("pause");
        return 0;
    }

![这里写图片描述][SouthEast 12]

4、比较操作  
![这里写图片描述][SouthEast 13]  
//在这里由于key值和value的值是一样的。方法也一样。

#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset1;
        set<int>::iterator it1;
        set<int>::reverse_iterator it2;
        set<int>::key_compare mycomp;//默认升序
        for (int i = 0; i < 5; i++)
        {
            myset1.insert(i * 10);
        }   
        it1 = myset1.begin();
        it2 = myset1.rbegin();
        int last = *it2;
        do
        {
            cout << " " << *it1;
        } while (mycomp(*it1++, last));
        system("pause");
        return 0;
    }

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**4、关于set一些其他操作：**  
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4.1：查找操作

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4.2 判断set中是否有值为key的元素

#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset1;
        set<int>::iterator it1;
        for (int i = 0; i < 5; i++)
        {
            myset1.insert(i);
        }   
        for (int i = 2; i < 6; i++)
        {
            cout << i;
            if (myset1.count(i)>0)
            {
                cout << "is in set" << endl;
            }
            else
            {
                cout << "is not in set" << endl;
            }
        }
            system("pause");
        return 0;
    }

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4.3  
lower\_bound(val): 返回容器中第一个值【大于或等于】val的元素的iterator位置。  
upper\_bound(val): 返回容器中第一个值【大于】val的元素的iterator位置。

#include<iostream>
    #include<stdlib.h>
    #include<set>
    using namespace std;
    int main()
    {
        set<int>myset1;
        set<int>::iterator it1;
        set<int>::iterator itlow;
        set<int>::iterator itupper;
        for (int i = 0; i < 5; i++)
        {
            myset1.insert(i);
        }
        itlow=myset1.lower_bound(2);
        itupper = myset1.upper_bound(3);
        cout << "itlow:" << *itlow << endl;
        cout <<"itupper:" <<*itupper << endl;
        system("pause");
        return 0;
    }

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