【POJ 2318】TOYS 叉积

用叉积判断左右

快速读入写错了卡了3小时hhh

#include<cmath>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define N 5003
#define read(x) x = getint()
using namespace std;
inline int getint() {
	int fh = 1, k = 0; char c = getchar();
	for(; c < '0' || c > '9'; c = getchar())
		if (c == '-') fh = -1;
	for(; c >= '0' && c <= '9'; c = getchar())
		k = k * 10 + c - '0';
	return k * fh;
}

struct Point {
	int x, y;
	Point(int _x = 0, int _y = 0) : x(_x), y(_y) {}
};
Point operator - (Point a, Point b) {
	return Point(a.x - b.x, a.y - b.y);
}
bool Cross(Point a, Point b) {
	return a.x * b.y - a.y * b.x > 0;
}

struct node {
	Point a, b;
};

Point toy;
node line[N];
int ans[N], n, m, up, left, down, right;

int main() {
	read(n);
	while (n) {
		read(m); read(left); read(up); read(right); read(down);
		for(int i = 1; i <= n; ++i) {
			scanf("%d%d", &line[i].a.x, &line[i].b.x);
			line[i].a.y = up;
			line[i].b.y = down;
		}

		for(int i = 0; i <= n; ++i)
			ans[i] = 0;

		while (m--) {
			read(toy.x); read(toy.y);
			int l = 1, r = n-1, mid, zuo, you;

			zuo = Cross(line[1].a - line[1].b, toy - line[1].b);
			you = Cross(line[n].a - line[n].b, toy - line[n].b);
			if (zuo) {
				++ans[0];
				continue;
			}
			if (!you) {
				++ans[n];
				continue;
			}

			while (l <= r) {
				mid = (l + r) >> 1;
				zuo = Cross(line[mid].a - line[mid].b, toy - line[mid].b);
				you = Cross(line[mid + 1].a - line[mid + 1].b, toy - line[mid + 1].b);
				if (zuo)
					r = mid - 1;
				else if (!you)
					 	l = mid + 1;
					 else
					 	break;
			}
			++ans[mid];
		}

		for(int i = 0; i <= n; ++i)
			printf("%d: %d\n", i, ans[i]);
		puts("");
		read(n);
	}

	return 0;
}

无语······