快速排序C++实现

来源：互联网发布：java中数组的定义编辑：程序博客网时间：2024/06/03 05:12

快速排序为原址排序，无需分配额外的Temp内存，且期望时间复杂度为O(nlgn)，可以通过交换数组中的第一个元素和随机一个元素的位置，达到随机化的目的，避开 bad case。

下面是C++实现，原数组元素存放在data.txt文件中：

选取第一个元素为主元

#include <stdio.h>#include <vector>#include <iostream>#include <fstream>#include <time.h>//快速排序法using namespace std;vector<int> d;  int count=0; static int CNT=0;//两个计数器记录比较的次数，用一个即可void printVector(const vector<int> &a){    for (int i = 0; i < a.size(); i++)    {        cout << a[i] << "  ";    }    cout << endl;}void swap_element(vector<int> &a, int i, int j){    int temp = a[i];    a[i] = a[j];    a[j] = temp;}int partition(vector<int> &a, int l, int r){    CNT+=r-l;    int i, j, x;    // i记录smaller和greater的分界线，j记录遍历位置 ，x记录主元的值    i = l , x = a[l];          //选取第一个元素为主元    for (j = l+1;j < r+1; j++)    {        ::count++;        if (a[j] < x)            swap_element(a, ++i, j);    }    swap_element(a, i, l);    return i;}void quick_Sort(vector<int> &a, int l,int r){    if (l < r)    {        int m = partition(a,l,r);        quick_Sort(a, l, m - 1);        quick_Sort(a, m + 1, r);    }}void ReadFromFile(){    extern vector<int> d;    fstream InFile("E:/QT/QuickSort/data.txt");    int ele = 0;    while (!InFile.eof())    {        InFile >> ele;        d.push_back(ele);    }    d.pop_back();}int main(){    clock_t start, end;    double totalTime;    start = clock();    //vector<int> ss{ 2,7,1,6,3,0,5,8,11,3,2,4,-1 };    //cout << "Unsort:  ";    //printVector(ss);    ReadFromFile();    cout << d.size() << endl;        system("pause");//暂停以确认是否完全都入    quick_Sort(d, 0, d.size()-1);    //cout << "Sorted:  ";    printVector(d);    cout<<endl<<" count : "<<::count<<endl;    cout<<endl<<" CNT : "<<CNT<<endl;    end = clock();    totalTime = (double)(end - start) / CLOCKS_PER_SEC;//记录程序运行时间    cout << endl<<" Total Running Time : " << totalTime  << " seconds !" << endl;    system("pause");    return 0;}

选取最后一个元素为主元

#include <stdio.h>#include <vector>#include <iostream>#include <fstream>#include <time.h>//快速排序法using namespace std;vector<int> d;int CNT = 0; static int count = 0;void printVector(const vector<int> &a){    for (int i = 0; i < a.size(); i++)    {        cout << a[i] << "  ";    }    cout << endl;}void swap_element(vector<int> &a, int i, int j){    int temp = a[i];    a[i] = a[j];    a[j] = temp;}int partition(vector<int> &a, int l, int r){       CNT += r - l;    int i, j, x;    i = l - 1, x = a[r];    //选取最后一个元素作为主元    for (j = l;j < r; j++)    {           ::count++;        if (a[j] < x)            swap_element(a, ++i, j);    }    swap_element(a, i + 1, r);    return i + 1;}void quick_Sort(vector<int> &a, int l,int r){    if (l < r)    {        int m = partition(a,l,r);        quick_Sort(a, l, m - 1);        quick_Sort(a, m + 1, r);    }}void ReadFromFile(){       extern vector<int> d;    fstream InFile("data.txt");    int ele = 0;    while (!InFile.eof())    {        InFile >> ele;        d.push_back(ele);    }}int main(){       clock_t start, end;    double totalTime;    start = clock();    //vector<int> ss{ 2,7,1,6,3,0,5,8,11,3,2,4,-1 };    //cout << "Unsort:  ";    //printVector(ss);    ReadFromFile();    cout << d.size() << endl;    system("pause");    quick_Sort(d, 0, d.size()-1);    //cout << "Sorted:  ";    printVector(d);    cout << endl << "CNT : "<<CNT << endl;    cout << endl << "count : " << ::count << endl;    end = clock();    totalTime = (double)(end - start) / CLOCKS_PER_SEC;    cout << "\nTotal Running Time :" << totalTime << "seconds！" << endl;    system("pause");    return 0;}

随机化，partition前将最后一个元素与随机位置元素交换数值

#include <stdio.h>#include <vector>#include <iostream>#include <fstream>#include <time.h>#include <stdlib.h>#define MIN 0//快速排序法using namespace std;vector<int> d;int CNT = 0; static int count = 0;void printVector(const vector<int> &a){    for (int i = 0; i < a.size(); i++)    {        cout << a[i] << "  ";    }    cout << endl;}void swap_element(vector<int> &a, int i, int j){       int temp = a[i];    a[i] = a[j];    a[j] = temp;}int partition(vector<int> &a, int l, int r){       srand((unsigned)time(NULL)); //初始化随机数种子     int MAX = a.size();    //cout << rand() % d.size() << endl;//控制随机数范围    int RAND = rand() % MAX;     swap_element(a,r, RAND); //随机交换    CNT += r - l;    int i, j, x;    i = l - 1, x = a[r];    //选取最后一个元素作为主元    for (j = l;j < r; j++)    {           ::count++;        if (a[j] < x)            swap_element(a, ++i, j);    }    swap_element(a, i + 1, r);    return i + 1;}void quick_Sort(vector<int> &a, int l,int r){    if (l < r)    {        int m = partition(a,l,r);        quick_Sort(a, l, m - 1);        quick_Sort(a, m + 1, r);    }}void ReadFromFile(){       extern vector<int> d;    fstream InFile("data.txt");    int ele = 0;    while (!InFile.eof())    {        InFile >> ele;        d.push_back(ele);    }}int main(){       clock_t start, end;    double totalTime;    start = clock();    //vector<int> ss{ 2,7,1,6,3,0,5,8,11,3,2,4,-1 };    //cout << "Unsort:  ";    //printVector(ss);    ReadFromFile();    cout << d.size() << endl;    system("pause");    quick_Sort(d, 0, d.size()-1);    //cout << "Sorted:  ";    printVector(d);    cout << endl << "CNT : "<<CNT << endl;    cout << endl << "count : " << ::count << endl;    end = clock();    totalTime = (double)(end - start) / CLOCKS_PER_SEC;    cout << "\nTotal Running Time :" << totalTime << "seconds！" << endl;    system("pause");    return 0;}

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