1.26

一、Map和Multimap

/*代码大致思路：
函数部分
print 输出一个map
printM 输出一个multimap
printG
printG_M
printL_M
*/
#include <iostream>
#include <map>
using namespace std;

typedef pair<int, double> CustomPair;

void print(map<int, double> &m)
{
    map<int, double>::iterator it;
    for(it = m.begin(); it != m.end(); it++)
    {
        CustomPair p1 = (CustomPair)(*it);
        cout << p1.first << ",";
        cout << std::fixed << cout.precision(2) <<  "," << p1.second << ';' << endl;
    }
}

void printM(multimap<int, double> &m)
{
    multimap<int, double>::iterator it;
    for(it = m.begin(); it != m.end(); it++)
    {
        CustomPair p1 = (CustomPair)(*it);
        cout << p1.first << ",";
        cout << std::fixed << cout.precision(2) << "," << p1.second << ';' << endl;
    }
}

void printG(map<int, double, greater<int> > &m)
{
    map<int, double, greater<int> >::iterator it;
    for(it = m.begin(); it != m.end(); it++)
    {
        CustomPair p1 = (CustomPair)(*it);
        cout << p1.first << ",";
        cout << std::fixed << cout.precision(2) << "," << p1.second << ';' << endl;
    }
}

void printG_M(multimap<int, double, greater<int> > &m)
{
    multimap<int, double, greater<int> >::iterator it;
    for(it = m.begin(); it != m.end(); it++)
    {
        CustomPair p1 = (CustomPair)(*it);
        cout << p1.first << ",";
        cout << std::fixed << cout.precision(2) << "," << p1.second << ';' << endl;
    }
}

void printL_M(map<int, double, less<int> > &m)
{
    map<int, double, greater<int> >::iterator it;
    for(it = m.begin(); it != m.end(); it++)
    {
        CustomPair p1 = (CustomPair)(*it);
        cout << p1.first << ",";
        cout << std::fixed << cout.precision(2) << "," << p1.second << ';' << endl;
    }
}

int main()
{
    map<int, double>::iterator itm;
    map<int, double, greater<int> >::iterator itmG;
    map<int, double, less<int> >::iterator itmL;

    map<int, double> m1;
    map<int, double, greater<int> > m2;
    multimap<int, double> m3;
    multimap<int, double, greater<int> > m4;

    m1.insert(CustomPair(1, 2.0));
    m1.insert(CustomPair(5, 5.0));
    m1.insert(CustomPair(3, 7.0));
    m1.insert(CustomPair(4, 8.0));
    m1.insert(CustomPair(5, 11.0));
    m1.insert(CustomPair(6, 6.0));
    cout << "m1:" << endl;
    print(m1);

    m2.insert(CustomPair(1, 2.0));
    m2.insert(CustomPair(5, 5.0));
    m2.insert(CustomPair(3, 7.0));
    m2.insert(CustomPair(4, 8.0));
    m2.insert(CustomPair(5, 11.0));
    m2.insert(CustomPair(6, 6.0));
    cout << "m2:" << endl;
    printG(m2);

    m3.insert(CustomPair(1, 2.0));
    m3.insert(CustomPair(5, 5.0));
    m3.insert(CustomPair(3, 7.0));
    m3.insert(CustomPair(4, 8.0));
    m3.insert(CustomPair(5, 11.0));
    m3.insert(CustomPair(6, 6.0));
    cout << "m3:" << endl;
    printM(m3);

    m4.insert(CustomPair(1, 2.0));
    m4.insert(CustomPair(5, 5.0));
    m4.insert(CustomPair(3, 7.0));
    m4.insert(CustomPair(4, 8.0));
    m4.insert(CustomPair(5, 11.0));
    m4.insert(CustomPair(6, 6.0));
    cout << "m4:" << endl;
    printG_M(m4);

    map<int, double>::allocator_type ma;
    ma = m2.get_allocator();
    map<int, double> m5(less<int>(), ma);

    m5.insert(CustomPair(16, 1.0));
    m5.insert(CustomPair(15, 7.0));
    m5.insert(CustomPair(24, 9.0));
    m5.insert(CustomPair(23, 12.0));
    m5.insert(CustomPair(32, 21.0));
    m5.insert(CustomPair(11, 27.0));

    cout << "m5:" << endl;
    printL_M(m5);

    cout << m1.size() << m1.max_size() << endl;

    return 0;
}

运行代码结果如下：

m1:
1,6,2.00;
3,2,7.00;
4,2,8.00;
5,2,5.00;
6,2,6.00;
m2:
6,2,6.00;
5,2,5.00;
4,2,8.00;
3,2,7.00;
1,2,2.00;
m3:
1,2,2.00;
3,2,7.00;
4,2,8.00;
5,2,5.00;
5,2,11.00;
6,2,6.00;
m4:
6,2,6.00;
5,2,5.00;
5,2,11.00;
4,2,8.00;
3,2,7.00;
1,2,2.00;
m5:
11,2,27.00;
15,2,7.00;
16,2,1.00;
23,2,12.00;
24,2,9.00;
32,2,21.00;
5134217727

1. 定义形式

map< key, Elem > m;
multimap< key, Elem > m;

2. pair类型

定义形式	说明
pair p1;	创建一个空的pair对象，它的两个元素对象分别是T1和T2类型，采用值初始化
pair p1(v1, v2);	创建一个pair对象，它的两个元素分别是T1和T2类型，其中first成员初始化为v1,而secon成员初始化为v2。
make_pair(v1, v2)	以v1和v2值创建一个新的对象，琪元素类型分别是v1和v2的类型
p1 < p2	两个pair对象之间的小于运算，其定义遵循字典次序：如果p1.first < p2.first 或者 p1.first >= p2.first && p1.second < p2.second，则返回true。
p1 == p2	两个pair对象的frist和second成员依次相等
p.first	返回p中的frist的数据成员
p.second	返回p中的second的数据成员

3. precision() 函数

precision()返回当前的浮点数的精度值，精度字段指定在小数点之前和之后的总数中要显示的最大有效位数。请注意，它不是最小值，因此如果数字显示的位数小于精度，则不会显示尾随零。

#include <iostream>  
#include <math.h>  

using namespace std;  

int main()  
{  
    double n;  
    cout<<"请输入一个数："<<endl;  
    cin>>n;  
    cout<<"对于"<<n<<"开平方的求解："<<endl;  
    double value = sqrt(n);  
    cout<<value<<endl;  
    for(int i=1;i<=9;i++)  
    {  
        cout.precision(i);  
        cout<<value<<endl;  
    }  
    return 0;  
}

运行代码结果如下：

请输入一个数：
3.0
对于3开平方的求解：
1.73205
2
1.7
1.73
1.732
1.7321
1.73205
1.732051
1.7320508
1.73205081

4. fixed函数

控制小数点后面的位数。

#include <iostream>

int main () {
  double a = 3.1415926534;
  double b = 2006.0;
  double c = 1.0e-10;

  std::cout.precision(5);

  std::cout << "default（默认）:\n";
  std::cout << a << '\n' << b << '\n' << c << '\n';

  std::cout << '\n';

  std::cout << "fixed（固定）:\n" << std::fixed;
  std::cout << a << '\n' << b << '\n' << c << '\n';

  std::cout << '\n';

  std::cout << "scientific（科学）:\n" << std::scientific;
  std::cout << a << '\n' << b << '\n' << c << '\n';
  return 0;
}

运行结果如下：

default（默认）:
3.1416
2006
1e-010

fixed（固定）:
3.14159
2006.00000
0.00000

scientific（科学）:
3.14159e+000
2.00600e+003
1.00000e-010

5. 成员函数

判空函数 empty( ) 若空返回true
遍历容器 begin() end( ) rbegin( ) rend( )

#include <iostream>
#include <map>

using namespace std;

typedef pair <int, double> mypair;

void Origin(map<int, double, greater<int> > &m, multimap<int, double, greater<int> > &mm)
{
    m.insert(mypair(1, 5.0));
    m.insert(mypair(2, 7.0));
    m.insert(mypair(3, 7.0));
    m.insert(mypair(4, 17.0));
    m.insert(mypair(5, 11.0));

    mm.insert(mypair(1, 4.0));
    mm.insert(mypair(2, 8.0));
    mm.insert(mypair(3, 9.0));
    mm.insert(mypair(4, 12.0));
    mm.insert(mypair(5, 19.0));
}

void print(map<int, double, greater<int> > &m, multimap<int, double, greater<int> > &mm)
{
    map<int, double, greater<int> >::iterator it;
    multimap<int, double, greater<int> >::iterator itM;

    int msize = m.size();
    cout << "map:" << msize << endl;
    for(it = m.begin(); it != m.end(); it++)
    {
        mypair temp = *it;
        cout << temp.first << "," <<temp.second << "," <<endl;
    }

    int mmsize = mm.size();
    cout << "multimap:" << mmsize << endl;
    for(itM = mm.begin(); itM != mm.end(); itM++)
    {
        mypair temp = *itM;
        cout << temp.first << "," <<temp.second << "," <<endl;
    }

    cout << endl;
}

int main()
{
    map<int, double, greater<int> > m1;
    multimap<int, double, greater<int> > m2;

    map<int, double, greater<int> >::iterator it;
    map<int, double, greater<int> >::reverse_iterator itR;

    multimap<int, double, greater<int> >::iterator itM;
    multimap<int, double, greater<int> >::reverse_iterator itRM;

    Origin(m1, m2);
    print(m1, m2);

    it = m1.begin();
    cout << (*it).first << "," << (*it).second << ";" << endl;

    it = m1.end();
    mypair temp = *(--it);
    cout << temp.first << "," << temp.second << ";" << endl;

    itM = m2.begin();
    cout << (*itM).first << "," << (*itM).second << ";" << endl;

    itM = m2.end();
    temp = *(--itM);
    cout << temp.first << "," << temp.second << ";" << endl;

    itR = m1.rbegin();
    cout << (*itR).first << "," << (*itR).second << ";" << endl;

    itR = m1.rend();
    temp = *(--itR);
    cout << temp.first << "," << temp.second << ";" << endl;

    itRM = m2.rbegin();
    cout << (*itRM).first << "," << (*itRM).second << ";" << endl;

    itRM = m2.rend();
    temp = *(--itRM);
    cout << temp.first << "," << temp.second << ";" << endl;

    return 0;
}

运行结果如下：

map:5
5,11,
4,17,
3,7,
2,7,
1,5,
multimap:5
5,19,
4,12,
3,9,
2,8,
1,4,

5,11;
1,5;
5,19;
1,4;
1,5;
5,11;
1,4;
5,19;

一、Map和Multimap

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