Add solution #509

Author: JoshCrozier

README.md

@@ -144,6 +144,7 @@
 476|[Number Complement](./0476-number-complement.js)|Easy|
 500|[Keyboard Row](./0500-keyboard-row.js)|Easy|
 506|[Relative Ranks](./0506-relative-ranks.js)|Easy|
+509|[Fibonacci Number](./0509-fibonacci-number.js)|Easy|
 520|[Detect Capital](./0520-detect-capital.js)|Easy|
 541|[Reverse String II](./0541-reverse-string-ii.js)|Easy|
 542|[01 Matrix](./0542-01-matrix.js)|Medium|

solutions/0509-fibonacci-number.js

@@ -0,0 +1,25 @@
+/**
+ * 509. Fibonacci Number
+ * https://leetcode.com/problems/fibonacci-number/
+ * Difficulty: Easy
+ *
+ * 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).
+ */
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var fib = function(n) {
+  const nums = [0, 1];
+
+  for (let i = 2; i <= n; i++) {
+    nums.push(nums[i - 2] + nums[i - 1]);
+  }
+
+  return nums[n];
+};