#509: Fibonacci Number; solution & tests

Author: vetalapo

c-sharp/Problems/math/FibonacciNumber.cs

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+/**
+ * 509
+ * Fibonacci Number
+ **
+ * The Fibonacci numbers,
+ * commonly denoted F(n) form a sequence,
+ * called the Fibonacci sequence,
+ * such that each number is the sum of the two preceding ones,
+ * starting from 0 and 1.
+ *
+ * That is,
+ *   F(0) = 0, F(1) = 1
+ *   F(n) = F(n - 1) + F(n - 2), for n > 1.
+ *
+ * Given n, calculate F(n).
+ *
+ * Example 1:
+ *   Input: n = 2
+ *   Output: 1
+ *   Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
+ *
+ * Example 2:
+ *   Input: n = 3
+ *   Output: 2
+ *   Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
+ *
+ * Example 3:
+ *   Input: n = 4
+ *   Output: 3
+ *   Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
+ *
+ * Constraints:
+ *   • 0 <= n <= 30
+ **
+ * https://leetcode.com/problems/fibonacci-number/
+***/
+
+namespace Problems;
+
+public class FibonacciNumber
+{
+    public int Fib( int n )
+    {
+        if ( n == 0 )
+        {
+            return 0;
+        }
+
+        int prev = 0;
+        int result = 1;
+
+        while ( n-- > 1 )
+        {
+            (prev, result) = (result, result + prev);
+        }
+
+        return result;
+    }
+}

c-sharp/Tests/math/FibonacciNumberTests.cs

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+using NUnit.Framework;
+
+using Problems;
+
+public class FibonacciNumberTests
+{
+    [TestCase( 2, ExpectedResult = 1 )]
+    [TestCase( 3, ExpectedResult = 2 )]
+    [TestCase( 4, ExpectedResult = 3 )]
+    [TestCase( 0, ExpectedResult = 0 )]
+    public int FibTest( int n ) =>
+        new FibonacciNumber().Fib( n );
+}