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Оптимално местоположение на точката за минимизиране на общото разстояние

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Дадено е множество от точки като и права като ax+by+c = 0. Трябва да намерим точка на дадена права, за която сборът от разстояния от даден набор от точки е минимален. 

Пример:  



In above figure optimum location of point of x - y - 3 = 0 line is (2 -1) whose total distance with other points is 20.77 which is minimum obtainable total distance.
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Ако вземем една точка на дадена линия на безкрайно разстояние, тогава общата цена на разстоянието ще бъде безкрайна сега, когато преместим тази точка на линията към дадени точки, общата цена на разстоянието започва да намалява и след известно време отново започва да нараства, което достига до безкрайност в другия безкраен край на линията, така че кривата на разходите за разстояние изглежда като U-крива и трябва да намерим най-долната стойност на тази U-крива. 

Тъй като U-кривата не се увеличава или намалява монотонно, ние не можем да използваме двоично търсене за намиране на най-долната точка тук, ще използваме троично търсене за намиране на най-долната точка, троичното търсене пропуска една трета от пространството за търсене при всяка итерация, можете да прочетете повече за троичното търсене тук

И така, решението продължава по следния начин, започваме с ниско и високо, инициализирани съответно като някои най-малки и най-големи стойности, след което започваме итерация във всяка итерация, изчисляваме две средни mid1 и mid2, които представляват 1/3-та и 2/3-та позиция в пространството за търсене, изчисляваме общото разстояние на всички точки с mid1 и mid2 и актуализираме ниско или високо, като сравняваме тези разходи за разстояние, тази итерация продължава, докато ниското и високото станат приблизително равни. 

C++
// C/C++ program to find optimum location and total cost #include    using namespace std; #define sq(x) ((x) * (x)) #define EPS 1e-6 #define N 5 // structure defining a point struct point {  int x y;  point() {}  point(int x int y)  : x(x)   y(y)  {  } }; // structure defining a line of ax + by + c = 0 form struct line {  int a b c;  line(int a int b int c)  : a(a)   b(b)   c(c)  {  } }; // method to get distance of point (x y) from point p double dist(double x double y point p) {  return sqrt(sq(x - p.x) + sq(y - p.y)); } /* Utility method to compute total distance all points  when choose point on given line has x-coordinate  value as X */ double compute(point p[] int n line l double X) {  double res = 0;  // calculating Y of chosen point by line equation  double Y = -1 * (l.c + l.a * X) / l.b;  for (int i = 0; i < n; i++)  res += dist(X Y p[i]);  return res; } // Utility method to find minimum total distance double findOptimumCostUtil(point p[] int n line l) {  double low = -1e6;  double high = 1e6;  // loop until difference between low and high  // become less than EPS  while ((high - low) > EPS) {  // mid1 and mid2 are representative x co-ordiantes  // of search space  double mid1 = low + (high - low) / 3;  double mid2 = high - (high - low) / 3;  //  double dist1 = compute(p n l mid1);  double dist2 = compute(p n l mid2);  // if mid2 point gives more total distance  // skip third part  if (dist1 < dist2)  high = mid2;  // if mid1 point gives more total distance  // skip first part  else  low = mid1;  }  // compute optimum distance cost by sending average  // of low and high as X  return compute(p n l (low + high) / 2); } // method to find optimum cost double findOptimumCost(int points[N][2] line l) {  point p[N];  // converting 2D array input to point array  for (int i = 0; i < N; i++)  p[i] = point(points[i][0] points[i][1]);  return findOptimumCostUtil(p N l); } // Driver code to test above method int main() {  line l(1 -1 -3);  int points[N][2] = {  { -3 -2 } { -1 0 } { -1 2 } { 1 2 } { 3 4 }  };  cout << findOptimumCost(points l) << endl;  return 0; } 
Java
// A Java program to find optimum location // and total cost class GFG {  static double sq(double x) { return ((x) * (x)); }  static int EPS = (int)(1e-6) + 1;  static int N = 5;  // structure defining a point  static class point {  int x y;  point() {}  public point(int x int y)  {  this.x = x;  this.y = y;  }  };  // structure defining a line of ax + by + c = 0 form  static class line {  int a b c;  public line(int a int b int c)  {  this.a = a;  this.b = b;  this.c = c;  }  };  // method to get distance of point (x y) from point p  static double dist(double x double y point p)  {  return Math.sqrt(sq(x - p.x) + sq(y - p.y));  }  /* Utility method to compute total distance all points  when choose point on given line has x-coordinate  value as X */  static double compute(point p[] int n line l  double X)  {  double res = 0;  // calculating Y of chosen point by line equation  double Y = -1 * (l.c + l.a * X) / l.b;  for (int i = 0; i < n; i++)  res += dist(X Y p[i]);  return res;  }  // Utility method to find minimum total distance  static double findOptimumCostUtil(point p[] int n  line l)  {  double low = -1e6;  double high = 1e6;  // loop until difference between low and high  // become less than EPS  while ((high - low) > EPS) {  // mid1 and mid2 are representative x  // co-ordiantes of search space  double mid1 = low + (high - low) / 3;  double mid2 = high - (high - low) / 3;  double dist1 = compute(p n l mid1);  double dist2 = compute(p n l mid2);  // if mid2 point gives more total distance  // skip third part  if (dist1 < dist2)  high = mid2;  // if mid1 point gives more total distance  // skip first part  else  low = mid1;  }  // compute optimum distance cost by sending average  // of low and high as X  return compute(p n l (low + high) / 2);  }  // method to find optimum cost  static double findOptimumCost(int points[][] line l)  {  point[] p = new point[N];  // converting 2D array input to point array  for (int i = 0; i < N; i++)  p[i] = new point(points[i][0] points[i][1]);  return findOptimumCostUtil(p N l);  }  // Driver Code  public static void main(String[] args)  {  line l = new line(1 -1 -3);  int points[][] = { { -3 -2 }  { -1 0 }  { -1 2 }  { 1 2 }  { 3 4 } };  System.out.println(findOptimumCost(points l));  } } // This code is contributed by Rajput-Ji 
Python3
# A Python3 program to find optimum location # and total cost import math class Optimum_distance: # Class defining a point class Point: def __init__(self x y): self.x = x self.y = y # Class defining a line of ax + by + c = 0 form class Line: def __init__(self a b c): self.a = a self.b = b self.c = c # Method to get distance of point  # (x y) from point p def dist(self x y p): return math.sqrt((x - p.x) ** 2 + (y - p.y) ** 2) # Utility method to compute total distance # all points when choose point on given # line has x-coordinate value as X def compute(self p n l x): res = 0 y = -1 * (l.a*x + l.c) / l.b # Calculating Y of chosen point # by line equation for i in range(n): res += self.dist(x y p[i]) return res # Utility method to find minimum total distance def find_Optimum_cost_untill(self p n l): low = -1e6 high = 1e6 eps = 1e-6 + 1 # Loop until difference between low # and high become less than EPS while((high - low) > eps): # mid1 and mid2 are representative x # co-ordiantes of search space mid1 = low + (high - low) / 3 mid2 = high - (high - low) / 3 dist1 = self.compute(p n l mid1) dist2 = self.compute(p n l mid2) # If mid2 point gives more total  # distance skip third part if (dist1 < dist2): high = mid2 # If mid1 point gives more total # distance skip first part else: low = mid1 # Compute optimum distance cost by  # sending average of low and high as X return self.compute(p n l (low + high) / 2) # Method to find optimum cost def find_Optimum_cost(self p l): n = len(p) p_arr = [None] * n # Converting 2D array input to point array for i in range(n): p_obj = self.Point(p[i][0] p[i][1]) p_arr[i] = p_obj return self.find_Optimum_cost_untill(p_arr n l) # Driver Code if __name__ == '__main__': obj = Optimum_distance() l = obj.Line(1 -1 -3) p = [ [ -3 -2 ] [ -1 0 ] [ -1 2 ] [ 1 2 ] [ 3 4 ] ] print(obj.find_Optimum_cost(p l)) # This code is contributed by Sulu_mufi 
C#
// C# program to find optimum location // and total cost using System; class GFG {  static double sq(double x) { return ((x) * (x)); }  static int EPS = (int)(1e-6) + 1;  static int N = 5;  // structure defining a point  public class point {  public int x y;  public point() {}  public point(int x int y)  {  this.x = x;  this.y = y;  }  };  // structure defining a line  // of ax + by + c = 0 form  public class line {  public int a b c;  public line(int a int b int c)  {  this.a = a;  this.b = b;  this.c = c;  }  };  // method to get distance of  // point (x y) from point p  static double dist(double x double y point p)  {  return Math.Sqrt(sq(x - p.x) + sq(y - p.y));  }  /* Utility method to compute total distance  of all points when choose point on  given line has x-coordinate value as X */  static double compute(point[] p int n line l  double X)  {  double res = 0;  // calculating Y of chosen point  // by line equation  double Y = -1 * (l.c + l.a * X) / l.b;  for (int i = 0; i < n; i++)  res += dist(X Y p[i]);  return res;  }  // Utility method to find minimum total distance  static double findOptimumCostUtil(point[] p int n  line l)  {  double low = -1e6;  double high = 1e6;  // loop until difference between  // low and high become less than EPS  while ((high - low) > EPS) {  // mid1 and mid2 are representative  // x co-ordiantes of search space  double mid1 = low + (high - low) / 3;  double mid2 = high - (high - low) / 3;  double dist1 = compute(p n l mid1);  double dist2 = compute(p n l mid2);  // if mid2 point gives more total distance  // skip third part  if (dist1 < dist2)  high = mid2;  // if mid1 point gives more total distance  // skip first part  else  low = mid1;  }  // compute optimum distance cost by  // sending average of low and high as X  return compute(p n l (low + high) / 2);  }  // method to find optimum cost  static double findOptimumCost(int[ ] points line l)  {  point[] p = new point[N];  // converting 2D array input to point array  for (int i = 0; i < N; i++)  p[i] = new point(points[i 0] points[i 1]);  return findOptimumCostUtil(p N l);  }  // Driver Code  public static void Main(String[] args)  {  line l = new line(1 -1 -3);  int[ ] points = { { -3 -2 }  { -1 0 }  { -1 2 }  { 1 2 }  { 3 4 } };  Console.WriteLine(findOptimumCost(points l));  } } // This code is contributed by 29AjayKumar 
JavaScript
<script> // A JavaScript program to find optimum location // and total cost function sq(x) {  return x*x; } let EPS = (1e-6) + 1; let N = 5; // structure defining a point class point {  constructor(xy)  {  this.x=x;  this.y=y;  } } // structure defining a line of ax + by + c = 0 form class line {  constructor(abc)  {  this.a = a;  this.b = b;  this.c = c;  }   } // method to get distance of point (x y) from point p function dist(xyp) {  return Math.sqrt(sq(x - p.x) + sq(y - p.y)); } /* Utility method to compute total distance all points  when choose point on given line has x-coordinate  value as X */ function compute(pnlX) {  let res = 0;    // calculating Y of chosen point by line equation  let Y = -1 * (l.c + l.a * X) / l.b;  for (let i = 0; i < n; i++)  res += dist(X Y p[i]);    return res; } // Utility method to find minimum total distance function findOptimumCostUtil(pnl) {  let low = -1e6;  let high = 1e6;    // loop until difference between low and high  // become less than EPS  while ((high - low) > EPS) {  // mid1 and mid2 are representative x  // co-ordiantes of search space  let mid1 = low + (high - low) / 3;  let mid2 = high - (high - low) / 3;    let dist1 = compute(p n l mid1);  let dist2 = compute(p n l mid2);    // if mid2 point gives more total distance  // skip third part  if (dist1 < dist2)  high = mid2;    // if mid1 point gives more total distance  // skip first part  else  low = mid1;  }    // compute optimum distance cost by sending average  // of low and high as X  return compute(p n l (low + high) / 2); } // method to find optimum cost function findOptimumCost(pointsl) {  let p = new Array(N);    // converting 2D array input to point array  for (let i = 0; i < N; i++)  p[i] = new point(points[i][0] points[i][1]);    return findOptimumCostUtil(p N l); } // Driver Code let l = new line(1 -1 -3); let points= [[ -3 -2 ]  [ -1 0 ]  [ -1 2 ]  [ 1 2 ]  [ 3 4 ]]; document.write(findOptimumCost(points l)); // This code is contributed by rag2127 </script> 

Изход
20.7652

Времева сложност: O(n2
Помощно пространство: O(n)