CareerCup

Check whether the given array follows the Fibonacci property.
eg if we are given 23,34,56,....
we know it cant be in Fibo seq as 23+34!=56

In case the given numbers follow the property
we can use the definition of Fibo seq..
F(n+1)=F(n)+F(n-1)
=> F(n-1) = F(n+1) - F(n)

in this if we go down then we should get 2,1,0 as last (+) nums.

eg for 23,34,57,....
other nums 'ld be 11,12,-1
so not in Fibo

Here is one written in Java,

public static boolean checkFibonacci (int array[])
{


for (int i=0; i < array.length/2; i++)
{

if(array[i] + array[i+1] ! = array [i+2])
{
return false;
}
}
if( array.length % 2 !=0 )
{
if (array[length -1] != array[length -2] + array[length -3])
{
return false;
}
}

return true;

}

public class isFibonacci{
public static void main(String args[]){
//int [] arr = {1,1,2,3,5,8,13,21,34,55,89,144};
int [] arr = {1,1,2,3,5,8,13,21,34,55,89,144};
int sum=0;
int i=1;
boolean flag = false;
while(i<arr.length-1){
sum =arr[i]+arr[i-1];
if(sum!=arr[i+1]){
flag=false;
System.out.println("Not a fibonacci sequence.");
break;
}
i++;
flag = true;
}
if(flag) System.out.println("A valid fiboncaai sequence.");
}
}

N is a Fibonacci number if and only if (5*N*N + 4) or (5*N*N - 4) is a perfect square.

class FibonacciChecker {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		int[] data={1,1,2,3,5,8,13};
		System.out.println("isFib : "+isFibonacci(data));
	}
	
	public static boolean isFibonacci(int[] data)
	{
		for(int i=2;i<data.length;i++)
		{
			int sum=data[i-2]+data[i-1];
			if(sum!=data[i])
				return false;
		}
		return true;
	}

}

class FibonacciChecker {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		int[] data={1,4,5,9};
		System.out.println("isFibonacci : "+isFibonacci(data));
	}
	
	private static boolean isFibonacci(int[] data)
	{
		if(data.length<2)
			return false;
		if(!checkForStartingNumbers(data[0])||!checkForStartingNumbers(data[1]))
			return false;
		for(int i=2;i<data.length;i++)
		{
			int sum=data[i-2]+data[i-1];
			if(sum!=data[i])
				return false;
		}
		return true;
	}
	
	private static boolean checkForStartingNumbers(int number)
	{
		int n=5*number*number+4;
		int n1=5*number*number-4;
		int sqrt1st=(int)Math.sqrt(n);
		int sqrt2nd=(int)Math.sqrt(n1);
		if(n==sqrt1st*sqrt1st||n1==sqrt2nd*sqrt2nd)
			return true;
		return false;
	}