poj 3432 --直接看上一篇2002吧。

同一个题目，不一样的形式，见上一篇2002的分析：

#include <iostream>
using namespace std;

struct Node
{
	int x,y;
	Node * next;
}node[40001];

int n;
int cod[2005][2];
int Find(int x, int y)
{
	int key = (x * x + y * y) % 40001;
	Node *tmp = &node[key];
	while (tmp->next != NULL)
	{
		tmp = tmp->next;
		if (tmp->x == x && tmp->y == y)
		{
			return 1;
		}
	}
	return 0;
}
int main()
{
	while (scanf("%d", &n) != EOF/*&& n*/)
	{
		memset(node, 0, sizeof(node));
		Node * point;
		for (int i = 1; i <= n; ++ i) 
		{
			point = new Node;
			scanf("%d %d", &cod[i][0], &cod[i][1]);
			point->x = cod[i][0];
			point->y = cod[i][1];
			point->next = NULL;

			int key = (cod[i][0] * cod[i][0] + cod[i][1] * cod[i][1]) % 40001;
			Node *tmp = &node[key];
			while (tmp->next != NULL)
			{
				tmp = tmp->next;
			}
			tmp->next = point;
		}

		int ans = 0;
		int x1,y1,x2,y2;
		for (int i = 1; i < n; ++ i)
		{
			for (int j = i + 1; j <= n; ++ j)
			{
				//two points on one side
				x1 = cod[i][0] + (cod[i][1] - cod[j][1]);
				y1 = cod[i][1] - (cod[i][0] - cod[j][0]);
				x2 = cod[j][0] + (cod[i][1] - cod[j][1]);
				y2 = cod[j][1] - (cod[i][0] - cod[j][0]);
				if (Find(x1,y1) && Find(x2,y2))
				{
					ans ++;
				}
				//
				x1 = cod[i][0] - (cod[i][1] - cod[j][1]);
				y1 = cod[i][1] + (cod[i][0] - cod[j][0]);
				x2 = cod[j][0] - (cod[i][1] - cod[j][1]);
				y2 = cod[j][1] + (cod[i][0] - cod[j][0]);
				if (Find(x1,y1) && Find(x2,y2))
				{
					ans ++;
				}
			}
		}
		printf("%d\n", ans / 4);
	}
	return 0;
}