Add solution #747

Author: JoshCrozier

README.md

@@ -161,6 +161,7 @@
 733|[Flood Fill](./0733-flood-fill.js)|Easy|
 739|[Daily Temperatures](./0739-daily-temperatures.js)|Medium|
 746|[Min Cost Climbing Stairs](./0746-min-cost-climbing-stairs.js)|Easy|
+747|[Largest Number At Least Twice of Others](./0747-largest-number-at-least-twice-of-others.js)|Easy|
 762|[Prime Number of Set Bits in Binary Representation](./0762-prime-number-of-set-bits-in-binary-representation.js)|Easy|
 784|[Letter Case Permutation](./0784-letter-case-permutation.js)|Medium|
 791|[Custom Sort String](./0791-custom-sort-string.js)|Medium|

solutions/0747-largest-number-at-least-twice-of-others.js

@@ -0,0 +1,20 @@
+/**
+ * 747. Largest Number At Least Twice of Others
+ * https://leetcode.com/problems/largest-number-at-least-twice-of-others/
+ * Difficulty: Easy
+ *
+ * You are given an integer array nums where the largest integer is unique.
+ *
+ * Determine whether the largest element in the array is at least twice as much
+ * as every other number in the array. If it is, return the index of the largest
+ * element, or return -1 otherwise.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var dominantIndex = function(nums) {
+  const max = Math.max(...nums);
+  return nums.find(n => n !== max && n > max / 2) ? -1 : nums.indexOf(max);
+};