C++实现数组中求第K大数

参考：http://blog.csdn.net/hackbuteer1/article/details/6651804

#include<iostream>
using namespace std;
bool Inputvalid=true;
void swap(int *num1,int* num2)
{
int temp=*num1;
*num1=*num2;
*num2=temp;
}
bool checkInvalidarray(int* num,int length,int k)//第k大的数 
{
if(num==NULL||length<=0||k>length)
Inputvalid=false;
return Inputvalid;
}
int partition(int* num,int length,int start,int end)
{
int flag=num[end];//参考位
if(num==NULL||length<=0||start<0||end>=length)
throw new std::exception("Invalid Parameters");
int pahead=start-1;
for(int i=start;i<end;++i)
{
if(num[i]<flag)
{
pahead++;
if(pahead!=i)
swap(&num[pahead],&num[i]);
}
}
++pahead;
swap(&num[pahead],&num[end]);
return pahead;
}
int FindKthNumber(int *num,int length,int k)
{
if(!checkInvalidarray(num,length,k))
return 0;
int index=partition(num,length,0,length-1);
int findindex=length-k;
while(index!=findindex)
{
if(index>findindex)
index=partition(num,length,0,index-1);
else
index=partition(num,length,index+1,length-1);
}
int result=num[index];
return result;
}
int main()
{
int num[]={1,10,7,3,2,9,5,4,8,6};
int KthNumber=FindKthNumber(num,10,5);
if(Inputvalid)
cout<<KthNumber<<endl;
else
cout<<"不合理输入"<<endl;
return 0;
}