寻找第k大数(快排思想)

剔除了相同的数，快排是从小到大排序的，所以k做了处理。

#include <iostream>
#include <cstdio>
using namespace std;

int hash[20000005]={0};
int A[10000005];
int counter=0;
int k;

int partition(int *A,int l,int r)
{
    int x=A[r];
    int i,j;
    int temp;
    i=l-1;
    for (j=l;j<=r-1;j++)
        if (A[j]<=x && j!=i)
        {
            i=i+1;
            temp=A[j];
            A[j]=A[i];
            A[i]=temp;
        }
    temp=A[i+1];
    A[i+1]=A[r];
    A[r]=temp;
    return i+1;
}

int quick_sort(int *A,int r)
{
  int mid;
  mid=partition(A,l,r);
  if (mid==k-1)
    return A[mid];
  else if (mid>k-1)
    return quick_sort(A,mid-1);
  else
    return quick_sort(A,mid+1,r);
}

int main()
{
  int n;
  scanf("%d%d",&n,&k);
  int i;
  int a;

  for (i=0;i<=n-1;i++)
  {
    scanf("%d",&a);
    if (!hash[a+10000000])
    {
    	hash[a+10000000]=1;
    	A[counter++]=a;
    }
  }

  k=counter-k+1;
  printf("%dn",quick_sort(A,counter-1));

  return 0;
}