STL sort升序排序小发现

来源：互联网发布：java程序员电脑配置编辑：程序博客网时间：2024/06/06 16:26

今天做了个小测试,发现sort函数第三个参数不应该添加,添加之后反而效率更低了.

比如说,一般情况下,要将N个数升序排列,sort(arr,arr+arr.length(),cmp) 这个cmp函数是这样的:

bool cmp(int a,int b)
{
return a>b;
}

这样就可以使序列升序,但是效率没有sort(arr,arr+arr.length());reverse(arr,arr+arr.length());效率高.

Test Code:

#include<iostream>#include<algorithm>#include<windows.h>#include<ctime>#define N 100000using namespace std;LARGE_INTEGER t1,t2,tc;void begin(){QueryPerformanceFrequency(&tc);QueryPerformanceCounter(&t1);}void end(){QueryPerformanceCounter(&t2);cout<<1.0*(t2.QuadPart-t1.QuadPart)/tc.QuadPart<<endl;}inline bool cmp(int a,int b){return a>b;}int main(){srand(time(0));int i,arr[N],arr1[N];for(i=0;i<N;i++){arr[i]=rand()%999+1;arr1[i]=arr[i];}begin();sort(arr,arr+N);reverse(arr,arr+N);end();begin();sort(arr1,arr1+N,cmp);end();return 0;}

Test result:

0.0585591
0.106811
请按任意键继续. . .

0 0