《算法导论》8、快速排序实现（C++）

来源：互联网发布：虚拟网络传销中的三虚编辑：程序博客网时间：2024/04/30 09:27

首先上一个正常版的，这种版本的程序对于升序或者降序的数组，会达到最差情况。

#include <iostream>#include <stdlib.h>  #include <time.h>using namespace std;int partition(int* A, int p, int r){if (p < r){int x = A[r];int i=p-1, j;int temp;for (j = p; j < r; j++){if (A[j] <= x){i++;temp = A[i];A[i] = A[j];A[j] = temp;}}temp = A[i + 1];A[i + 1] = A[r];A[r] = temp;return i + 1;}}void quickSort(int* A, int p, int r){if (p < r){int q = partition(A, p, r);quickSort(A, p, q - 1);quickSort(A, q + 1, r);}}void main(){int n = 100000;  //排序元素长度  int* A = new int[n];for (int i = 0; i <n; i++){A[i] = rand() % 1000;}clock_t start, finish;double totaltime;start = clock();quickSort(A,0,n-1);finish = clock();totaltime = (double)(finish - start) / CLOCKS_PER_SEC;/*for (int i = 0; i < n; i++){cout << A[i] << "  ";}cout << endl;*/cout << "堆排序的运行时间为" << totaltime << "秒！" << endl;system("pause");}

然后上一个随机版本的，随机就是在使用快排之前，先对数组进行随机化处理。

但是这样太2了，所以我的策略是（其实是书上抄的），随机选取r，然后和最后一位交换位置。

#include <iostream>#include <stdlib.h>  #include<time.h>using namespace std;int partition(int* A, int p, int r){if (p < r){int r1 = (rand() % (r - p + 1)) + p;int temp=A[r1];A[r1] = A[r];A[r] = temp;int x = A[r];int i=p-1, j;for (j = p; j < r; j++){if (A[j] <= x){i++;temp = A[i];A[i] = A[j];A[j] = temp;}}temp = A[i + 1];A[i + 1] = A[r];A[r] = temp;return i + 1;}}void quickSort(int* A, int p, int r){if (p < r){int q = partition(A, p, r);quickSort(A, p, q - 1);quickSort(A, q + 1, r);}}void main(){int n = 100000;  //排序元素长度  int* A = new int[n];for (int i = 0; i <n; i++){A[i] = rand() % 1000;}clock_t start, finish;double totaltime;start = clock();quickSort(A,0,n-1);finish = clock();totaltime = (double)(finish - start) / CLOCKS_PER_SEC;/*for (int i = 0; i < n; i++){cout << A[i] << "  ";}cout << endl;*/cout << "堆排序的运行时间为" << totaltime << "秒！" << endl;system("pause");}

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