POJ 2318 TOYS 二分+叉积

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入门计算几何

判断在哪个区域内只需看跟某条线的叉积即可

可以保证单调性，所以可以进行二分

#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <algorithm>#include <cstdlib>#include <cmath>#include <map>#include <sstream>#include <queue>#include <vector>#define MAXN 100001#define MAXM 211111#define eps 1e-8#define INF 500000001using namespace std;int dblcmp(double d){    if(fabs(d) < eps) return 0;    return d > eps ? 1 : -1;}struct point{    double x, y;    point(){}    point(double _x, double _y):    x(_x), y(_y) {};    void input()    {        scanf("%lf%lf", &x, &y);    }    void output()    {        printf("%.2f %.2f\n", x, y);    }    double det(point p)    {        return x * p.y - y * p.x;    }    point sub(point p)    {        return point(x - p.x, y - p.y);    }}up[5555], down[5555];double getcross(point a, point o, point b){    a = a.sub(o);    b = b.sub(o);    return a.det(b);}int num[5555];int n, m;int main(){    double xa, xb, ya, yb, ui, li;    int cas = 0;    while(scanf("%d", &n) != EOF && n)    {        scanf("%d%lf%lf%lf%lf", &m, &xa, &ya, &xb, &yb);        if(cas++) puts("");        up[0] = point(xa, ya);        down[0] = point(xa, yb);        for(int i = 1; i <= n; i++)        {            scanf("%lf%lf", &ui, &li);            up[i] = point(ui, ya);            down[i] = point(li, yb);        }        up[n + 1] = point(xb, ya);        down[n + 1] = point(xb, yb);        memset(num, 0, sizeof(num));        point tmp;        for(int i = 0; i < m; i++)        {            tmp.input();            int low = 0, high = n + 1;            while(low <= high)            {                int mid = (low + high) >> 1;                if(dblcmp(getcross(up[mid], tmp, down[mid])) > 0)                    low = mid + 1;                else high = mid - 1;            }            num[low - 1] ++;        }        for(int i = 0; i <= n; i++) printf("%d: %d\n", i, num[i]);    }    return 0;}