C ++ STL的Map和Multimap中的降序
通常，映射和多映射映射的默认行为是按升序存储元素。但是我们可以使用更大的功能按降序存储元素。
映射降序排列：
这里使用的功能-
m::find()–如果找到，则返回映射中键值为“b”的元素的迭代器，否则返回迭代器结束。
m::erase()–从映射上移除键值。
m::equal_range()–返回成对的迭代器。该对是指范围的边界，该范围包括容器中所有具有与key等效的key的元素。
minsert()–在映射容器中插入元素。
msize()–返回映射容器中的元素数。
mcount()–返回映射中键值为“a”或“f”的元素的匹配数。
范例程式码
#include <iostream>
#include <map>
#include <string>
using namespace std;
int main () {
map<char, int,greater <int>> m;
map<char, int>::iterator it;
m.insert (pair<char, int>('a', 10));
m.insert (pair<char, int>('b', 20));
m.insert (pair<char, int>('c', 30));
m.insert (pair<char, int>('d', 40));
cout<<"Size of the map: "<< m.size() <<endl;
cout << "map contains:\n";
for (it = m.begin(); it != m.end(); ++it)
cout << (*it).first << " => " << (*it).second << '\n';
for (char c = 'a'; c <= 'd'; c++) {
cout << "There are " << m.count(c) << " element(s) with key " << c << ":";
map<char, int>::iterator it;
for (it = m.equal_range(c).first; it != m.equal_range(c).second; ++it)
cout << ' ' << (*it).second;
cout << endl;
}
if (m.count('a'))
cout << "The key a is present\n";
else
cout << "The key a is not present\n";
if (m.count('f'))
cout << "The key f is present\n";
else
cout << "The key f is not present\n";
it = m.find('b');
m.erase (it);
cout<<"Size of the map: "<<m.size()<<endl;
cout << "map contains:\n";
for (it = m.begin(); it != m.end(); ++it)
cout << (*it).first << " => " << (*it).second << '\n';
return 0;
}输出结果
Size of the map: 4 map contains: d => 40 c => 30 b => 20 a => 10 There are 1 element(s) with key a: 10 There are 1 element(s) with key b: 20 There are 1 element(s) with key c: 30 There are 1 element(s) with key d: 40 The key a is present The key f is not present Size of the map: 3 map contains: d => 40 c => 30 a => 10
多图按降序排列：
在这里使用函数：
mm::find()–如果找到，则返回在多映射中具有键值“b”的元素的迭代器，否则返回迭代器结束。
mm::erase()–从多重映射中删除键值。
mm::equal_range()–返回成对的迭代器。该对是指范围的边界，该范围包括容器中所有具有与key等效的key的元素。
mminsert()–在多图容器中插入元素。
mmsize()–返回多图容器中的元素数。
范例程式码
#include <iostream>
#include <map>
#include <string>
using namespace std;
int main () {
multimap<char, int,greater <char>> mm;
multimap<char, int>::iterator it;
mm.insert (pair<char, int>('a', 10));
mm.insert (pair<char, int>('b', 20));
mm.insert (pair<char, int>('a', 30));
mm.insert (pair<char, int>('b', 40));
cout<<"Size of the multimap: "<< mm.size() <<endl;
cout << "multimap contains:\n";
for (it = mm.begin(); it != mm.end(); ++it)
cout << (*it).first << " => " << (*it).second << '\n';
for (char c = 'a'; c <= 'd'; c++) {
cout << "There are " << mm.count(c) << " elements with key " << c << ":";
map<char, int>::iterator it;
for (it = mm.equal_range(c).first; it != mm.equal_range(c).second; ++it)
cout << ' ' << (*it).second;
cout << endl;
}
if (mm.count('a'))
cout << "The key a is present\n";
else
cout << "The key a is not present\n";
if (mm.count('f'))
cout << "The key f is present\n";
else
cout << "The key f is not present\n";
it = mm.find('b');
mm.erase (it);
cout<<"Size of the multimap: "<<mm.size()<<endl;
cout << "multiap contains:\n";
for (it = mm.begin(); it != mm.end(); ++it)
cout << (*it).first << " => " << (*it).second << '\n';
return 0;
}输出结果
Size of the multimap: 4 multimap contains: b => 20 b => 40 a => 10 a => 30 There are 2 elements with key a: 10 30 There are 2 elements with key b: 20 40 There are 0 elements with key c: There are 0 elements with key d: The key a is present The key f is not present Size of the multimap: 3 multiap contains: b => 40 a => 10 a => 30