CCF 202006-1 线性分类器

代码1：正常思路+STL

/*线性分类器*/
#include 
#include 
using namespace std;
typedef long long LL; //此处是关键

struct point{
	int xn, yn;
	char c;
};
vector<point> a; //存储A类点
vector<point> b; //存储B类点

int main()
{
	int n, m, cnta = 0, cntb = 0;
	cin >> n >> m;
	for(int i = 0; i < n; i ++)
	{
		int x, y;
		char c;
		point p;
		cin >> x >> y >> c;
		p.xn = x;
		p.yn = y;
		if(c == 'A'){
			a.push_back(p);
		}
		if(c == 'B'){
			b.push_back(p);
		}	
	}
	
	for(int i = 0; i < m; i ++)
	{
		int a0, a1, a2, t = 0;
        LL cala, calb, cal; //此处要用long long类型，因为下面两个函数值相乘可能会超出int的范围
		cin >> a0 >> a1 >> a2;
		
		cala = a0 + a1*a[0].xn + a2*a[0].yn;
		calb = a0 + a1*b[0].xn + a2*b[0].yn;
		
		for(int j = 0; j < a.size(); j ++)
		{
			cal = a0 + (LL)a1*a[j].xn + (LL)a2*a[j].yn;
			if(cal*cala > 0)
				t ++;
			else
				break;
		}
		
		for(int k = 0; k < b.size(); k ++)
		{
			cal = a0 + (LL)a1*b[k].xn + (LL)a2*b[k].yn;
			if(cal*calb > 0)
				t ++;
			else
				break;
		}
		if(t == n && cala*calb < 0) cout << "Yes" << endl;
		else cout << "No" << endl;
	}
	return 0;
}

代码2：简洁思路+结构体

/*线性分类器*/
#include 
using namespace std;

const int N = 1000 + 5;

struct point{
	int xn, yn;
	char v;
}a[N];

int main()
{
	int n, m;
	cin >> n >> m;
	for(int i = 0; i < n; i ++)
	{
		cin >> a[i].xn >> a[i].yn >> a[i].v;
	}
	
	for(int i = 0; i < m; i ++)
	{
		int a0, a1, a2;
		int A, B;
		cin >> a0 >> a1 >> a2;
		for(int j = 0; j < n; j ++)
		{
			if(a[0].v == 'A')//判定A、B在直线的哪一侧
			{
				if(a0 + a1*a[0].xn + a2*a[0].yn > 0){
					A = 1, B = -1;//这样可以避免函数值超出int范围
				}else{
					A = -1, B = 1;
				}
			}
			if(a[0].v == 'B')
			{
				if(a0 + a1*a[0].xn + a2*a[0].yn > 0){
					B = 1, A = -1;
				}else{
					B = -1, A = 1;
				}
			}		
		}
		int t = 1;
		for(int j = 1; j < n; j ++)
		{
			if(a[j].v == 'A')
			{
				if((a0 + a1*a[j].xn + a2*a[j].yn)*A > 0){
					t ++;
				}else{
					break;
				}	
			}
			if(a[j].v == 'B')
			{
				if((a0 + a1*a[j].xn + a2*a[j].yn)*B > 0){
					t ++;
				}else{
					break;
				}	
			}
		}	
		if(t == n) cout << "Yes" << endl;
		else cout << "No" << endl;
	}
	return 0;
}