pku1971.cpp

这是ACM 方面的资料 是PKU的 北京大学的出来的

#include <stdio.h>
#include <stdlib.h>

typedef struct 
{
	int x, y;
} Point;

Point p[1000], midp[1000000];

int cmp(const void *a, const void *b)
{
	Point *aa = (Point *)a;
	Point *bb = (Point *)b;

	if (aa->x == bb->x)
	{
		return aa->y - bb->y;
	}
	else
	{
		return aa->x - bb->x;
	}
}

int main()
{
	int t, n;
	int i, j, k;
	int total;

	scanf("%d", &t);

	while (t--)
	{
		scanf("%d", &n);
		total = 0;

		for (i = 0; i < n; i++)
		{
			scanf("%d %d", &p[i].x, &p[i].y);
		}

		for (i = 0, k = 0; i < n - 1; i++)
		{
			for (j = i + 1; j < n; j++)
			{
				midp[k].x = p[i].x + p[j].x;
				midp[k].y = p[i].y + p[j].y;
				k++;
			}
		}

		qsort(midp, n * (n - 1) / 2, sizeof(midp[0]), cmp);

		for (i = 1, j = 1; i < n * (n - 1) / 2; i++)
		{
			if (midp[i-1].x == midp[i].x && midp[i-1].y == midp[i].y)
			{
				j++;
			}
			else
			{
				total += (j - 1) * j / 2;
				j = 1;
			}
		}
		total += (j - 1) * j / 2;

		printf("%d\n", total);
	}
	
	return 0;
}