算法导论—快排及优化以及和STL sort 的比较

#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

//当元素少的时候可以采用插入排序
void insertSort(vector<int> &vec,int left,int right)
{
int i;
for(int j=left+1;j<=right;++j)
{
int key=vec[j];
for(i=j-1;i>=left&&vec[i]>key;--i)
vec[i+1]=vec[i];
vec[i+1]=key;
}
}

//取中位数作为最右边的主元
void median3(vector<int> &vec,int p,int r)
{
int center=(p+r)/2;

if(vec[center]<vec[p])
std::swap(vec[center],vec[p]);

if(vec[r]<vec[p])
std::swap(vec[r],vec[p]);

if(vec[r]>vec[center])
std::swap(vec[center],vec[r]);
}

int partition(vector<int> &vec,int p,int r)
{
median3(vec,p,r);
int x=vec[r];
int i,j;
i=p-1;
for(j=p;j<r;++j)
{
if(vec[j]<x)
{
i=i+1;
std::swap(vec[i],vec[j]);
}
}
std::swap(vec[i+1],vec[r]);
return i+1;
}

void qSort(vector<int> &vec,int p,int r)
{
if(p+10<r)
{
int q=partition(vec,p,r);
qSort(vec,p,q-1);
qSort(vec,q+1,r);
}
else
insertSort(vec,p,r);
}

int main()
{
vector<int> vec{19,7,4,5,188,1,0,56,5};

qSort(vec,0,vec.size()-1);
for(auto v:vec)
cout<<v<<" ";
cout<<endl;
vector<int> vec1;
vector<int> vec2;

int val;
ifstream in;
in.open("rand_file_5000W");
while(in>>val)
{
vec1.push_back(val);
vec2.push_back(val);
}

in.close();

clock_t start_time=clock();

qSort(vec1,0,vec1.size()-1);

clock_t end_time=clock();

cout<<"Running time is: "<<
static_cast<double>(end_time-start_time)/CLOCKS_PER_SEC<<" S"<<endl;

clock_t start_time2=clock();
sort(vec2.begin(),vec2.end());
clock_t end_time2=clock();

cout<<"Running time is: "<<
static_cast<double>(end_time2-start_time2)/CLOCKS_PER_SEC<<" S"<<endl;

int flag=1;
for(int i=0;i<=vec1.size()-1;++i)
{
if(vec1[i]!=vec2[i])
flag=0;
}
if(flag==1)
cout<<"right"<<endl;

}