# Java Challenge - Fibonacci Finder

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Iteration:

public static int fibFinder(int n) {
if (n == 0) {
return 0;
}
if (n == 1) {
return 1;
}
int n1 = 0;
int n2 = 1;
int n3;
int count = 2;
while (count <= n) {
n3 = n2 + n1;
count++;
n1 = n2;
n2 = n3;
}
return n2;
}

1 Like

Dynamic Programming:

private static int fib(int n, HashMap<Integer, Integer> record) {
if (n == 0) {
return 0;
}
if (n == 1) {
return 1;
}
if (record.containsKey(n)) {
return record.get(n);
}
int n2 = fib(n - 2, record);
int n1 = fib(n - 1, record);
int result = n1 + n2;
record.put(n, result);
return result;
}

public static int fibFinder(int n) {
return fib(n, new HashMap<Integer, Integer>());
}

public class FibonacciFinder {
public static void main(String args) {
System.out.print(fibFinder(6));
}

public static int fibFinder(int n) {
int num1=0, num2=1;
for(int i=0;i<n;i++) {
int num3 = num1+num2;
num1=num2;
num2=num3;

``````}
``````

return num1;
}

}

public class FibonacciFinder {
public static void main(String args) {
System.out.print(fibFinder(6));
}

public static int fibFinder(int n) {
double a = 1 + Math.pow(5,0.5);
double b = 1 - Math.pow(5,0.5);
double x = (Math.pow(a,n) - Math.pow(b,n)) / (Math.pow(2,n) * (a - 1));
return (int)x;
}
}

This it was my first challenge, and it has cost me more than I thought. Here is my solution:

``````public class FibonacciFinder {
public static void main(String[] args) {
System.out.print(fibFinder(6));
}

public static int fibFinder(int n) {
// resultado = sumandoA + sumandoB
int sumandoA = 1;
int sumandoB = 0;
if (n == 0 || n == 1) {
return n;
}else{
int count = 2;
while (count <= n) {
count++;
sumandoB = sumandoA;
}
}
}
}
``````
``````public class FibonacciFinder {
public static void main(String[] args) {
System.out.print(fibFinder(6));
}

public static int fibFinder(int n) {
int num1 = 0;
int num2 = 1;
int newNum = 1;
if(n == 0 || n == 1){
return n;
}

for(int i = 2; i < n; i++){
num1 = num2;
num2= newNum;
newNum = num1 + num2;
}
return newNum;
}
}
``````

I tried some dynamic programming stuff from the lesson … memoization
I used the `FibonnaciFinder` object to store an array containing the Fibonacci Sequence numbers found so far,
and I created methods for those objects (including some extras) so it looks more object-oriented.

``````public class FibonacciFinder {

public int[] sequence;  // for memoization
public int length = 0;  // keeps track of length of stuff already done

public FibonacciFinder() {
this.sequence = new int[0];
this.length = 0;
}
public FibonacciFinder(int n) {
this.sequence = new int[n + 1];
if (n >= 0) {
this.sequence[0] = 0;
this.length = 1;
}
if (n >= 1) {
this.sequence[1] = 1;
this.length = 2;
}
}

public int size() {
return this.length;
}

public int get(int j) {
if (j < this.length) {
return this.sequence[j];
}
else {
// recursion:
int value = this.get(j - 1) + this.get(j - 2);
this.sequence[j] = value;
this.length++;
return value;
}
}
public int get() {
if (this.length < this.sequence.length) {
return this.get(this.length);
}
else {
return this.sequence[this.sequence.length - 1];
}
}

public static int fibFinder(int n) {
if (n < 0) {
return 0;
}
else if (n <= 1) {
return n;
}
else {
FibonacciFinder finder = new FibonacciFinder(n);
return finder.get(n);
}
}

public static void main(String[] args) {
System.out.println(fibFinder(6));
}

}
``````

I guess a simpler version of that (but using a loop instead of recursion) would be:

``````  public static int fib(int n) {
if (n <= 1) {
return n;
}
int[] a = new int[n + 1]; // memo for sequence
a[0] = 0;
a[1] = 1;
for (int i = 2; i <= n; i++) {
a[i] = a[i - 1] + a[i - 2];
}
return a[n];
}
``````

I know I could have done that using an ArrayList or some kind of map instead.

public class FibonacciFinder {
public static void main(String args) {
System.out.print(fibFinder(6));
}

/**
Fibonacci sequence number finder implemented using recursion
*/
public static int fibFinder(int n) {
if(n==0)
{
return 0;
}
else if(n==1)
{
return 1;
}
else
{
return fibFinder(n-2)+fibFinder(n-1);
}

}
}

My one liner using recursion:

``````public static int fibFinder(int n) {
return n > 1 ? fibFinder(n-1) + fibFinder(n-2) : n;
}
``````