Java Challenge - Fibonacci Finder

FAQ
#1

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#2

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
#3

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>());
}

#4

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;
}

}

#5

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

public static int fibFinder(int n) {
// Write your code here
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;
}
}

#6

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 resultado = 0;
    int sumandoA = 1;
    int sumandoB = 0;
    if (n == 0 || n == 1) {
      return n;
      }else{
        int count = 2;
        while (count <= n) {
        resultado = sumandoA + sumandoB;
        count++;
        sumandoB = sumandoA;
        sumandoA = resultado;
        }
        return resultado; 
      }
    }
}
#7 
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;
  }
}
#8

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.