UVa 1595 - Symmetry

题目

判断一个平面上的点是不是关于某条竖线对称。

分析

计算几何。首先利用所有点的横坐标的和计算出折线对应的x，然后将左右分成两组，将x坐标转化成相对折线的距离，排序比较输出。

说明

好多书和论文要看，还要学英语。。。ε=(´ο｀*)))唉

#include <algorithm>
#include <iostream>
#include <cstdio>

using namespace std;

typedef struct _point
{
	double x, y;
}point;

point P[1001];
point L[1001];
point R[1001];

bool cmp(point a, point b)
{
	if (a.x == b.x) {
		return a.y < b.y;
	} else {
		return a.x < b.x;
	}
}

int main()
{
	int T, N;
	while (~scanf("%d", &T)) 
	while (T --) {
		scanf("%d", &N);
		double sum = 0.0;
		for (int i = 0; i < N; ++ i) {
			scanf("%lf%lf", &P[i].x, &P[i].y);
			sum += P[i].x;
		}
		
		double mid = sum / N;
		int lcount = 0, rcount = 0;
		for (int i = 0; i < N; ++ i) {
			if (P[i].x < mid) {
				L[lcount].x = mid - P[i].x;
				L[lcount].y = P[i].y;
				lcount ++;
			}
			if (P[i].x > mid) {
				R[rcount].x = P[i].x - mid;
				R[rcount].y = P[i].y;
				rcount ++;
			}
		}
		
		int flag = 0;
		if (lcount == rcount) {
			sort(L, L + lcount, cmp);
			sort(R, R + rcount, cmp);
			flag = 1;
			for (int i = 0; i < lcount; ++ i) {
				if (L[i].x != R[i].x || L[i].y != R[i].y) {
					flag = 0;
					break;
				}
			}

		}
		
		if (flag) {
			puts("YES");
		} else {
			puts("NO");		
		}
	} 
	return 0;
}