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Sunday, 28 August 2016

Chapter 8 Exercise 8, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

**8.8 (All closest pairs of points) Revise Listing 8.3, FindNearestPoints.java, to display all closest pairs of points with the same minimum distance. Here is a sample run: Enter the number of points: 8 Enter 8 points: 0 0 1 1 -1 -1 2 2 -2 -2 -3 -3 -4 -4 5 5 The closest two points are (0.0, 0.0) and (1.0, 1.0) The closest two points are (0.0, 0.0) and (-1.0, -1.0) The closest two points are (1.0, 1.0) and (2.0, 2.0) The closest two points are (-1.0, -1.0) and (-2.0, -2.0) The closest two points are (-2.0, -2.0) and (-3.0, -3.0) The closest two points are (-3.0, -3.0) and (-4.0, -4.0) Their distance is 1.4142135623730951 



import java.util.Scanner;
 
public class ProgramingEx8_8 {
 public static void main(String[] args) {
  Scanner input = new Scanner(System.in);
  System.out.print("Enter the number of points: ");
  int numberOfPoints = input.nextInt();
 
  // Create an array to store points
  double[][] points = new double[numberOfPoints][2];
  int[][] sortestPoints = new int[numberOfPoints][2];
  System.out.print("Enter " + numberOfPoints + " points: ");
  for (int i = 0; i < points.length; i++) {
   points[i][0] = input.nextDouble();
   points[i][1] = input.nextDouble();
  }
 
  // p1 and p2 are the indices in the points array
  int p1 = 0, p2 = 1, n = 0; // Initial two points and shortest distance
         // array index (n)
  sortestPoints[n][0] = p1;
  sortestPoints[n][1] = p2;
  double shortestDistance = distance(points[p1][0], points[p1][1],
    points[p2][0], points[p2][1]); // Initialize shortestDistance
 
  // Compute distance for every two points
  for (int i = 0; i < points.length; i++) {
   for (int j = i + 1; j < points.length; j++) {
    double distance = distance(points[i][0], points[i][1],
      points[j][0], points[j][1]); // Find distance
 
    // check the difference between the distance and the shortest
    // distance to a threshold
    if (Math.abs(shortestDistance - distance) < 10e-6) {
     // new pair for points with shortest distance found
     n++;
     sortestPoints[n][0] = i;
     sortestPoints[n][1] = j;
 
    } else if (shortestDistance > distance) {// New shortest
               // distance found
 
     n = 0;
     sortestPoints[n][0] = i;
     sortestPoints[n][1] = j;
     shortestDistance = distance; // Update shortestDistance
    }
   }
  }
 
  // Display result
  for (int i = 0; i < n + 1; i++) {
 
   p1 = sortestPoints[i][0];
   p2 = sortestPoints[i][1];
 
   System.out.println("The closest two points are " + "("
     + points[p1][0] + ", " + points[p1][1] + ") and ("
     + points[p2][0] + ", " + points[p2][1] + ")");
  }
 
  System.out.println("Their distance is " + shortestDistance);
 
 }
 
 /** Compute the distance between two points (x1, y1) and (x2, y2) */
 public static double distance(double x1, double y1, double x2, double y2) {
  return Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
 }
}

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