FibonacciNumber

Maths/FactorialRecursion.java

@@ -0,0 +1,26 @@
+package Maths;
+
+public class FactorialRecursion {
+
+    /* Driver Code */
+    public static void main(String[] args) {
+        assert factorial(0) == 1;
+        assert factorial(1) == 1;
+        assert factorial(2) == 2;
+        assert factorial(3) == 6;
+        assert factorial(5) == 120;
+    }
+
+    /**
+     * Recursive FactorialRecursion Method
+     *
+     * @param n The number to factorial
+     * @return The factorial of the number
+     */
+    public static long factorial(int n) {
+        if (n < 0) {
+            throw new IllegalArgumentException("number is negative");
+        }
+        return n == 0 || n == 1 ? 1 : n * factorial(n - 1);
+    }
+}

Maths/FibonacciNumber.java

@@ -0,0 +1,37 @@
+package Maths;
+
+/**
+ * Fibonacci: 0 1 1 2 3 5 8 13 21 ...
+ */
+public class FibonacciNumber {
+    public static void main(String[] args) {
+        assert isFibonacciNumber(1);
+        assert isFibonacciNumber(2);
+        assert isFibonacciNumber(21);
+        assert !isFibonacciNumber(9);
+        assert !isFibonacciNumber(10);
+    }
+
+    /**
+     * Check if a number is perfect square number
+     *
+     * @param number the number to be checked
+     * @return <tt>true</tt> if {@code number} is perfect square, otherwise <tt>false</tt>
+     */
+    public static boolean isPerfectSquare(int number) {
+        int sqrt = (int) Math.sqrt(number);
+        return sqrt * sqrt == number;
+    }
+
+    /**
+     * Check if a number is fibonacci number
+     * This is true if and only if at least one of 5x^2+4 or 5x^2-4 is a perfect square
+     *
+     * @param number the number
+     * @return <tt>true</tt> if {@code number} is fibonacci number, otherwise <tt>false</tt>
+     * @link https://en.wikipedia.org/wiki/Fibonacci_number#Identification
+     */
+    public static boolean isFibonacciNumber(int number) {
+        return isPerfectSquare(5 * number * number + 4) || isPerfectSquare(5 * number * number - 4);
+    }
+}

Others/CountChar.java

@@ -2,13 +2,6 @@ package Others;
 
 import java.util.Scanner;
 
-
-/**
- * @author blast314
- * <p>
- * Counts the number of characters in the text.
- */
-
 public class CountChar {
 
     public static void main(String[] args) {
@@ -20,11 +13,12 @@ public class CountChar {
     }
 
     /**
-     * @param str: String to count the characters
+     * Count non space character in string
-     * @return int: Number of characters in the passed string
+     *
+     * @param str String to count the characters
+     * @return number of character in the specified string
      */
     private static int CountCharacters(String str) {
-    	str = str.replaceAll("\\s","");
+        return str.replaceAll("\\s", "").length();
-        return str.length();
     }
 }

Others/Factorial.java

@@ -1,50 +0,0 @@
-package Others;
-
-import java.util.Scanner;
-
-/**
- * This program will print out the factorial of any non-negative
- * number that you input into it.
- *
- * @author Marcus
- */
-public class Factorial {
-
-    /**
-     * The main method
-     *
-     * @param args Command line arguments
-     */
-    public static void main(String[] args) {
-        Scanner input = new Scanner(System.in);
-        System.out.print("Enter a non-negative integer: ");
-
-        //If user does not enter an Integer, we want program to fail gracefully, letting the user know why it terminated
-        try {
-            int number = input.nextInt();
-
-            //We keep prompting the user until they enter a positive number
-            while (number < 0) {
-                System.out.println("Your input must be non-negative. Please enter a positive number: ");
-                number = input.nextInt();
-            }
-            //Display the result
-            System.out.println("The factorial of " + number + " will yield: " + factorial(number));
-
-        } catch (Exception e) {
-            System.out.println("Error: You did not enter an integer. Program has terminated.");
-        }
-        input.close();
-    }
-
-    /**
-     * Recursive Factorial Method
-     *
-     * @param n The number to factorial
-     * @return The factorial of the number
-     */
-    public static long factorial(int n) {
-        if (n == 0 || n == 1) return 1;
-        return n * factorial(n - 1);
-    }
-}