Add solution #724

Author: JoshCrozier

README.md

@@ -233,6 +233,7 @@
 706|[Design HashMap](./0706-design-hashmap.js)|Easy|
 713|[Subarray Product Less Than K](./0713-subarray-product-less-than-k.js)|Medium|
 722|[Remove Comments](./0722-remove-comments.js)|Medium|
+724|[Find Pivot Index](./0724-find-pivot-index.js)|Easy|
 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|

solutions/0724-find-pivot-index.js

@@ -0,0 +1,34 @@
+/**
+ * 724. Find Pivot Index
+ * https://leetcode.com/problems/find-pivot-index/
+ * Difficulty: Easy
+ *
+ * Given an array of integers nums, calculate the pivot index of this array.
+ *
+ * The pivot index is the index where the sum of all the numbers strictly to the left
+ * of the index is equal to the sum of all the numbers strictly to the index's right.
+ *
+ * If the index is on the left edge of the array, then the left sum is 0 because there
+ * are no elements to the left. This also applies to the right edge of the array.
+ *
+ * Return the leftmost pivot index. If no such index exists, return -1.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var pivotIndex = function(nums) {
+  let left = 0;
+  let right = nums.reduce((sum, n) => sum + n, 0);
+
+  for (let i = 0; i < nums.length; i++) {
+    left += nums[i];
+    right -= nums[i];
+    if (left - nums[i] === right) {
+      return i;
+    }
+  }
+
+  return -1;
+};