Competitive Programming

/**
 * Author: Ulf Lundstrom
 * Date: 2009-03-21
 * License: CC0
 * Source: Basic math
 * Description:\\
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Returns the signed distance between point p and the line containing points a and b. Positive value on left side and negative on right as seen from a towards b. a==b gives nan. P is supposed to be Point<T> or Point3D<T> where T is e.g. double or long long. It uses products in intermediate steps so watch out for overflow if using int or long long. Using Point3D will always give a non-negative distance.
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\includegraphics[width=\textwidth]{../content/geometry/lineDistance}
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 * Status: tested 
 */
#pragma once

#include "Point.h"

template <class P>
double lineDist(const P& a, const P& b, const P& p) {
	return (double)(b-a).cross(p-a)/(b-a).dist();
}