unordered

• • 测试代码
  • 比较
  • • N=1000
    • N=10000
    • N=100000
    • N=1000000
    • N=10000000
    • N=100000000
  • 小结

下面这段代码可以比较unordered_set和set增删查的性能

以下数据都是在VS2022 release版本下测的

#include 
#include 
#include 
#include 
#include 
#include 
using namespace std;
#define N 10000000
void test()
{
	srand(time(0));
	vectorv;
	v.reserve(N);
	for (int i = 0; i < N; i++)
	{
		v.push_back(rand());
	}

	sets;
	unordered_setus;
//------------------------------------------
	//set insert time
	clock_t begin1 = clock();
	for (int i = 0; i < N; i++)
	{
		s.insert(v[i]);
	}
	clock_t end1 = clock();

	//unorde_set insert time
	clock_t begin2 = clock();
	for (int i = 0; i < N; i++)
	{
		us.insert(v[i]);
	}
	clock_t end2 = clock();
	cout << "set insert: " << end1 - begin1 << endl;
	cout << "unordered_set insert: " << end2 - begin2 << endl << endl;
//------------------------------------------
	//set find time
	clock_t begin3 = clock();
	for (auto e : v)
	{
		s.find(e);
	}
	clock_t end3 = clock();

	clock_t begin4 = clock();
	for (auto e : v)
	{
		us.find(e);
	}
	clock_t end4 = clock();
	cout << "set find: " << end3 - begin3 << endl;
	cout << "unordered_set find: " << end4 - begin4 << endl << endl;
//------------------------------------------

	//set erase time
	clock_t begin5 = clock();
	for (auto e : v)
	{
		s.erase(e);
	}
	clock_t end5 = clock();

	//unordered_set erase time
	clock_t begin6 = clock();
	for (auto e : v)
	{
		us.erase(e);
	}
	clock_t end6 = clock();

	cout << "set earse: " << end5- begin5 << endl;
	cout << "unordered_set erase: " << end6 - begin6 << endl << endl;
}

int main()
{
	test();

	return 0;
}

可以看到unordered_set在增删查方面的性能都比set好，但是为什么我们不用unordered_set去代替set呢？因为set还有一个特点就是有序！而在底层方面，unordered_set底层是哈希，set是红黑树。

处理无序数据时建议用unordered_set，如果需要有序那就选set