快排 QSORT

快排最坏情况下运行时间为O(n²)，平均情况运行时间为O(n*log₂n)。演示程序如下：

#include <iostream>#include <stdlib.h>#include <ctime>using namespace std;int partition(int *A,int p,int r){int i,j,x;x=A[r];i=p-1;for(j=p;j<r;j++)if(A[j] <= x){i++;swap<int>(A[i],A[j]);}swap<int>(A[i+1],A[r]);return i+1;}void quicksort(int *A,int p,int r){if(p >= r)return ;int q=partition(A,p,r);quicksort(A,p,q-1);quicksort(A,q+1,r);}void Show(int *A,int p,int r){for(int i=p;i<=r;i++)cout<<A[i]<<" ";cout<<endl;}int main(){int i;int A[10];srand((unsigned int)time(NULL));for(i=0;i<10;i++)A[i]=rand()%20;Show(A,0,9);quicksort(A,0,9);Show(A,0,9);system("pause");return 0;}