multiset是可重复关键字的关联式容器,其与序列式容器相比最大的优势在于其查找效率相当高。(牺牲空间换取时间段)
例程
#include<stdexcept>
#include<string>
#include<cstdlib>
#include<cstdio>
#include<algorithm>
#include<iostream>
#include<ctime>
#include<set>
using namespace std;
long get_a_target_long()
{
long target = 0;
cout<<"target(0~"<<RAND_MAX<<"):";
cin>>target;
return target;
}
string get_a_target_string()
{
long target = 0;
char buf[10];
cout<<"target(0~"<<RAND_MAX<<"):";
cin>>target;
snprintf(buf, 10, "%ld", target);
return string(buf);
}
int compareLongs(const void* a, const void* b)
{
return (*(long*)a - *(long*)b);
}
int compareStrings(const void *a, const void *b)
{
if(*(string*)a > *(string*)b)
return 1;
else if(*(string*)a < *(string*)b)
return -1;
else
return 0;
}
void test_multiset(long& value)
{
cout << "\ntest_multiset().......... \n";
multiset<string> c;
char buf[10];
clock_t timeStart = clock();
for(long i=0; i< value; ++i)
{
try
{
snprintf(buf, 10, "%d", rand());//multiset可以采用rand()方式填写元素,而set则不可以
c.insert(string(buf));
}
catch(exception& p)
{
cout << "i=" << i << " " << p.what() << endl;
abort();
}
}
cout << "milli-seconds : " << (clock()-timeStart) << endl;
cout << "multiset.size()= " << c.size() << endl; //元素个数
cout << "multiset.max_size()= " << c.max_size() << endl; //max_size大小和内存大小正相关
string target = get_a_target_string();
{
timeStart = clock();
auto pItem = find(c.begin(), c.end(), target); //查找比 c.find(...) 慢很多
cout << "std::find(), milli-seconds : " << (clock()-timeStart) << endl;
if (pItem != c.end())
cout << "found, " << *pItem << endl;
else
cout << "not found! " << endl;
}
{
timeStart = clock();
auto pItem = c.find(target); //查找比 std::find(...) 快很多
cout << "c.find(), milli-seconds : " << (clock()-timeStart) << endl;
if (pItem != c.end())
cout << "found, " << *pItem << endl;
else
cout << "not found! " << endl;
}
}
int main()
{
long int value;
cout<<"how many elements: ";
cin>>value;
test_multiset(value);
return 0;
}
运行结果