FibonacciNumber

Author: realDuYuanChao

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 @@
 
 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 static void main(String[] args) {
     }
 
     /**
-     * @param str: String to count the characters
-     * @return int: Number of characters in the passed string
+     * Count non space character in 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.length();
+        return str.replaceAll("\\s", "").length();
     }
 }