Change project structure to a Maven Java project + Refactor (#2816)

src/main/java/com/thealgorithms/maths/FibonacciNumber.java

@@ -0,0 +1,40 @@
+package com.thealgorithms.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);
+    }
+}