# Java Exercises: Compute the radius and the central coordinate of a circle

## Java Basic: Exercise-218 with Solution

Write a Java program to compute the radius and the central coordinate (x, y) of a circle which is constructed by three given points on the plane surface.

**Input: **

x1,y1,x2,y2,x3,y3,xp,yp separated by a single space.

**Sample Solution:**

**Java Code:**

```
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.BufferedReader;
class Main {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Input x1, y1, x2, y2, x3, y3 separated by a single space:");
String[] input = br.readLine().split(" ");
double x1 = Double.parseDouble(input[0]);
double y1 = Double.parseDouble(input[1]);
double x2 = Double.parseDouble(input[2]);
double y2 = Double.parseDouble(input[3]);
double x3 = Double.parseDouble(input[4]);
double y3 = Double.parseDouble(input[5]);
double A = x2 - x1;
double B = y2 - y1;
double p = (y2 * y2 - y1 * y1 + x2 * x2 - x1 * x1) / 2;
double C = x3 - x1;
double D = y3 - y1;
double q = (y3 * y3 - y1 * y1 + x3 * x3 - x1 * x1) / 2;
double X = (D * p - B * q) / (A * D - B * C);
double Y = (A * q - C * p) / (A * D - B * C);
double r = Math.sqrt(Math.pow(X - x1, 2.0) + Math.pow(Y - y1, 2.0));
System.out.println("\nRadius and the central coordinate:");
System.out.printf("%.3f (%.3f %.3f)", r, X, Y);
}
}
```

Sample Output:

Input x1, y1, x2, y2, x3, y3 separated by a single space: 5 6 4 8 7 9 Radius and the central coordinate: 1.821 (5.786 7.643)

**Flowchart: **

**Java Code Editor:**

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**Next:** Write a Java program to check if a point (x, y) is in a triangle or not. There is a triangle formed by three points.

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## Java: Tips of the Day

** How to remove leading zeros from alphanumeric text?**

Regex is the best tool for the job; what it should be depends on the problem specification. The following removes leading zeroes, but leaves one if necessary (i.e. it wouldn't just turn "0" to a blank string).

s.replaceFirst("^0+(?!$)", "")

The ^ anchor will make sure that the 0+ being matched is at the beginning of the input. The (?!$) negative lookahead ensures that not the entire string will be matched.

Test harness:

String[] in = { "01234", // "[1234]" "0001234a", // "[1234a]" "101234", // "[101234]" "000002829839", // "[2829839]" "0", // "[0]" "0000000", // "[0]" "0000009", // "[9]" "000000z", // "[z]" "000000.z", // "[.z]" }; for (String s : in) { System.out.println("[" + s.replaceFirst("^0+(?!$)", "") + "]"); }

Ref: https://bit.ly/2Qdcl8a

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