算法导论第7章—快速排序

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快速排序

#include<iostream>using namespace std;void Print(int *A,int p,int r){for(int i=p;i<=r;i++)cout<<A[i]<<" ";cout<<endl;}int Partition(int *A,int p,int r){int x=A[r];int i=p-1;for(int j=p;j<=r-1;j++){if(A[j]<=x){i++;swap(A[i],A[j]);}}swap(A[i+1],A[r]);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);}}int main(){int A[100];int p,r;cout<<"请输入p,q的值:";cin>>p>>r;cout<<"请输入数字：";for(int i=p;i<=r;i++)cin>>A[i];cout<<"快速排序前：";Print(A,p,r);cout<<"快速排序后：";QuickSort(A,p,r);Print(A,p,r);return 0;}

随机化版本：

#include<iostream>#include<ctime>#include<cstdlib>using namespace std;void Print(int *A,int p,int r){for(int i=p;i<=r;i++)cout<<A[i]<<" ";cout<<endl;}int Partition(int *A,int p,int r){int x=A[r];int i=p-1;for(int j=p;j<=r-1;j++){if(A[j]<=x){i++;swap(A[i],A[j]);}}swap(A[i+1],A[r]);return i+1;}int Randomized_Partition(int *A,int p,int r){srand(time(NULL));    //生成随机数int i=rand()%(r-p)+p;swap(A[r],A[i]);return Partition(A,p,r);}void Randomized_QuickSort(int *A,int p,int r){if(p<r){int q=Randomized_Partition(A,p,r);Randomized_QuickSort(A,p,q-1);Randomized_QuickSort(A,q+1,r);}}int main(){int A[100];int p,r;cout<<"请输入p,q的值:";cin>>p>>r;cout<<"请输入数字：";for(int i=p;i<=r;i++)cin>>A[i];cout<<"快速排序前：";Print(A,p,r);Randomized_QuickSort(A,p,r);cout<<"快速排序后：";Print(A,p,r);return 0;}

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