## 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));
}
}