算法3.11 采用分治算法计算中位数

#include 
#include 
using namespace std;

#define NUM 1001
int a[NUM];
int select(int left, int right, int k)
{
	if (left >= right) return a[left];
	int i = left;
	int j = right+1; 
	int pivot = a[left];
	while (true) 
	{
		do {
			i = i+1;
		} while (a[i] < pivot);
		do {
			j = j-1;
		} while (a[j] > pivot);
		if (i >= j) break;
		swap(a[i], a[j]);
	}
	if (j-left+1 == k) return pivot;
	a[left] = a[j];
	a[j] = pivot;
	if (j-left+1 < k)
	return select(j+1, right, k-j+left-1);
	else return select(left, j-1, k);
}

int main()
{
	int n;
	int x;
	int y;
	cin>>n;
	for (int i=0; i<n; i++)
		cin>>x>>a[i];
	y = select(0, n-1, n/2);
	int min=0;
	for(int i=0;i<n;i++)
		min += (int)fabs(a[i]-y);
	cout<<min<<endl;
	return 0;
}