count number of viewable points

angle.cpp

#include <vector>
#include <cmath>
#include <algorithm>

struct Point
{
	int x;
	int y;
};

auto getAngle(const Point& point)
{
	static constexpr double PI = 3.14159265;
	auto angle =  std::atan2(point.y, point.x) * (180.0 / PI);
	if (angle < 0)
	{
		angle += 360;
	}
	return angle;
}

int main()
{
	std::vector<Point> points{ { 1, 1 },{ 3,1 },{ 3,2 },{ 3, 3 },{ 1, 3 },{ 2, 5 },{ 1, 5 },{ -1, -1 },{ -1, -2 },{ -2, -3 },{ -4, -4 } };
	
	std::vector<int> angles;
	angles.resize(points.size());
	std::transform(points.begin(), points.end(), angles.begin(), [](auto point) {return getAngle(point); });
	std::sort(angles.begin(), angles.end());

	std::vector<int> count;
	count.reserve(angles.size());

	for (auto startAngleIt = angles.begin(); startAngleIt != angles.end(); ++startAngleIt)
	{
		auto endAngle = std::round(*startAngleIt + 45.0);
		auto endAngleIt = std::upper_bound(angles.begin(), angles.end(), endAngle);
		count.push_back(std::distance(startAngleIt, endAngleIt));
	}
    
	auto result = *std::max_element(count.begin(), count.end());

	return 0;
}