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