From b8f6f9d7f93cc7bdf0ffe8bdb5b0d8e3afd0d507 Mon Sep 17 00:00:00 2001
From: vatsalgosar <vatsalgosar@gmail.com>
Date: Thu, 5 Dec 2019 20:54:42 +0530
Subject: [PATCH] BAEL-3519 (#8169)

* BAEL-3519
- Fibonacci Series
- Recursive method
- Iterative method

* - Added new method that uses Golden Ratio to calculate the given term of Fibonacci Series

* added binet formula implementation of constant time for fibonacci term
---
 .../fibonacci/FibonacciSeriesUtils.java       | 34 +++++++++++++++++++
 .../FibonacciSeriesUtilsUnitTest.java         | 29 ++++++++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 java-numbers-2/src/main/java/com/baeldung/fibonacci/FibonacciSeriesUtils.java
 create mode 100644 java-numbers-2/src/test/java/com/baeldung/fibonacci/FibonacciSeriesUtilsUnitTest.java

diff --git a/java-numbers-2/src/main/java/com/baeldung/fibonacci/FibonacciSeriesUtils.java b/java-numbers-2/src/main/java/com/baeldung/fibonacci/FibonacciSeriesUtils.java
new file mode 100644
index 0000000000..943fcffa56
--- /dev/null
+++ b/java-numbers-2/src/main/java/com/baeldung/fibonacci/FibonacciSeriesUtils.java
@@ -0,0 +1,34 @@
+package com.baeldung.fibonacci;
+
+import static java.lang.Math.pow;
+
+public class FibonacciSeriesUtils {
+
+    public static int nthFibonacciTermRecursiveMethod(int n) {
+        if (n == 0 || n == 1) {
+            return n;
+        }
+        return nthFibonacciTermRecursiveMethod(n - 1) + nthFibonacciTermRecursiveMethod(n - 2);
+    }
+
+    public static int nthFibonacciTermIterativeMethod(int n) {
+        if (n == 0 || n == 1) {
+            return n;
+        }
+        int n0 = 0, n1 = 1;
+        int tempNthTerm;
+        for (int i = 2; i <= n; i++) {
+            tempNthTerm = n0 + n1;
+            n0 = n1;
+            n1 = tempNthTerm;
+        }
+        return n1;
+    }
+
+    public static int nthFibonacciTermUsingBinetsFormula(int n) {
+        final double squareRootOf5 = Math.sqrt(5);
+        final double phi = (1 + squareRootOf5)/2;
+        int nthTerm = (int) ((Math.pow(phi, n) - Math.pow(-phi, -n))/squareRootOf5);
+        return nthTerm;
+    }
+}
diff --git a/java-numbers-2/src/test/java/com/baeldung/fibonacci/FibonacciSeriesUtilsUnitTest.java b/java-numbers-2/src/test/java/com/baeldung/fibonacci/FibonacciSeriesUtilsUnitTest.java
new file mode 100644
index 0000000000..60f79d0c78
--- /dev/null
+++ b/java-numbers-2/src/test/java/com/baeldung/fibonacci/FibonacciSeriesUtilsUnitTest.java
@@ -0,0 +1,29 @@
+package com.baeldung.fibonacci;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class FibonacciSeriesUtilsUnitTest {
+
+    @Test
+    public void givenTermToCalculate_thenReturnThatTermUsingRecursion() {
+        int term = 10;
+        int expectedValue = 55;
+        assertEquals(FibonacciSeriesUtils.nthFibonacciTermRecursiveMethod(term), expectedValue);
+    }
+
+    @Test
+    public void givenTermToCalculate_thenReturnThatTermUsingIteration() {
+        int term = 10;
+        int expectedValue = 55;
+        assertEquals(FibonacciSeriesUtils.nthFibonacciTermIterativeMethod(term), expectedValue);
+    }
+
+    @Test
+    public void givenTermToCalculate_thenReturnThatTermUsingBinetsFormula() {
+        int term = 10;
+        int expectedValue = 55;
+        assertEquals(FibonacciSeriesUtils.nthFibonacciTermUsingBinetsFormula(term), expectedValue);
+    }
+}