poj2318(叉乘+二分)

矩形被n块板分割，有m个物品都在矩形里，求每一块的物品的个数

用叉乘判断物品在板的左右侧，在用二分查找第一块在物品右侧的板

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int mx = 5e3+5;
int u[mx], l[mx], ans[mx];

int calc(int x1, int y1, int x2, int y2) {
    return x1*y2 - x2*y1;
}

int main() {
	int n, m, x1, y1, x2, y2, flag = 0;
	while (scanf("%d%d%d%d%d%d",&n,&m,&x1,&y1,&x2,&y2) == 6) {
        if (flag) puts("");
        flag = 1;
        memset(ans, 0, sizeof(ans));
        for (int i = 0; i < n; i++) {
            scanf("%d%d",&u[i], &l[i]);
        }
        int x, y;
        for (int i = 1; i <= m; i++) {
            scanf("%d%d",&x,&y);
            int low = 0, high = n, mid;
            while (low < high) {
                mid = (low + high) / 2;
                if (calc(u[mid]-x, y1-y, l[mid]-x, y2-y) <= 0) high = mid;
                else low = mid + 1;
            }
            ans[low]++;
        }
        for (int i = 0; i <= n; i++) {
            printf("%d: %d\n",i, ans[i]);
        }

	}

    return 0;
}