面试：用快排实现数组中的第K大的数

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

 int selectKth(int a[],int start,int end,int k){
     assert(start <= end && k <= end+);
     int left = start;
     int right = end;
     int pivotVal = a[left];
     while(left < right){
         while(left < right && a[right] >= pivotVal) right--;
         a[left] = a[right];
         while(left < right && a[left] <= pivotVal) left++;
         a[right] = a[left];
     }
     a[left] = pivotVal;
     if(left+ == k) return a[left];
     else if(left+ < k) return selectKth(a,left+,end,k);
     else return selectKth(a,start,left-,k);
 }

 int main() {
     int a[] = {,,,,,,,};

     std::cout << selectKth(a,,,) << std::endl;
     std::cout << selectKth(a,,,) << std::endl;

     return ;
 }