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FibonacciNumber.java

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FibonacciNumber.java

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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);
}
}
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