Added different approaches to Fibonacci Numbers

Author: rampatra

src/main/java/com/ctci/recursionanddp/FibonacciNumber.java

@@ -0,0 +1,64 @@
+package com.ctci.recursionanddp;
+
+/**
+ * The fabled fibonacci numbers problem with three different solutions.
+ * The {@link FibonacciNumber#fibonacciBottomUpOptimized(int)} version is the most optimized among all w.r.t space
+ * and time. See {@link com.rampatra.dynamicprogramming.FibonacciNumbers} for Fibonacci series.
+ *
+ * @author rampatra
+ * @since 2019-02-26
+ */
+public class FibonacciNumber {
+
+    private static int fibonacciTopDown(int n, int[] memo) {
+        if (n == 0 || n == 1) return n;
+
+        if (memo[n] != 0) {
+            return memo[n];
+        } else {
+            memo[n] = fibonacciTopDown(n - 1, memo) + fibonacciTopDown(n - 2, memo);
+            return memo[n];
+        }
+    }
+
+    private static int fibonacciBottomUp(int n) {
+        if (n == 0 || n == 1) return n;
+
+        int[] memo = new int[n + 1];
+        memo[1] = 1;
+        for (int i = 2; i <= n; i++) {
+            memo[i] = memo[i - 1] + memo[i - 2];
+        }
+        return memo[n];
+    }
+
+    private static int fibonacciBottomUpOptimized(int n) {
+        if (n == 0 || n == 1) return n;
+
+        int a = 0;
+        int b = 1;
+        int res = a + b;
+
+        for (int i = 2; i <= n; i++) {
+            res = a + b;
+            a = b;
+            b = res;
+        }
+
+        return res;
+    }
+
+    public static void main(String[] args) {
+        System.out.println(fibonacciTopDown(4, new int[5]));
+        System.out.println(fibonacciBottomUp(4));
+        System.out.println(fibonacciBottomUpOptimized(4));
+        System.out.println("---");
+        System.out.println(fibonacciTopDown(5, new int[6]));
+        System.out.println(fibonacciBottomUp(5));
+        System.out.println(fibonacciBottomUpOptimized(5));
+        System.out.println("---");
+        System.out.println(fibonacciTopDown(10, new int[11]));
+        System.out.println(fibonacciBottomUp(10));
+        System.out.println(fibonacciBottomUpOptimized(10));
+    }
+}

src/main/java/com/rampatra/dynamicprogramming/FibonacciNumbers.java

@@ -9,7 +9,6 @@
  *
  * @author rampatra
  * @since 9/10/15
- * @time: 3:57 PM
  */
 public class FibonacciNumbers {
 
@@ -22,9 +21,9 @@ public class FibonacciNumbers {
      * @param k
      */
     public static int[] getFirstKFibonacciNumbers(int k) {
-        int[] fib = new int[k + 1];
+        int[] fib = new int[k];
         int i = 1;
-        while (i <= k) {
+        while (i < k) {
             if (i == 1 || i == 2) {
                 fib[i] = 1;
             } else {
@@ -35,7 +34,7 @@ public static int[] getFirstKFibonacciNumbers(int k) {
         return fib;
     }
 
-    public static void main(String a[]) {
+    public static void main(String[] a) {
         out.println(Arrays.toString(getFirstKFibonacciNumbers(0)));
         out.println(Arrays.toString(getFirstKFibonacciNumbers(10)));
         out.println(Arrays.toString(getFirstKFibonacciNumbers(46)));

src/main/java/com/rampatra/misc/DivideByZero.java

@@ -10,6 +10,6 @@
 public class DivideByZero {
     public static void main(String[] a) {
         System.out.println(5.0 / 0); // doesn't throw any exception
-        System.out.println(5 / 0); // throws runtime exception (arithmetic exception)
+        System.out.println(5 / 0); // throws runtime exception or unchecked exception (does NOT need explicit handling). To be specific, throws an arithmetic exception.
     }
-}
+}