Add solution #852

Author: JoshCrozier

README.md

@@ -659,6 +659,7 @@
 849|[Maximize Distance to Closest Person](./0849-maximize-distance-to-closest-person.js)|Medium|
 850|[Rectangle Area II](./0850-rectangle-area-ii.js)|Hard|
 851|[Loud and Rich](./0851-loud-and-rich.js)|Medium|
+852|[Peak Index in a Mountain Array](./0852-peak-index-in-a-mountain-array.js)|Medium|
 867|[Transpose Matrix](./0867-transpose-matrix.js)|Easy|
 868|[Binary Gap](./0868-binary-gap.js)|Easy|
 872|[Leaf-Similar Trees](./0872-leaf-similar-trees.js)|Easy|

solutions/0852-peak-index-in-a-mountain-array.js

@@ -0,0 +1,33 @@
+/**
+ * 852. Peak Index in a Mountain Array
+ * https://leetcode.com/problems/peak-index-in-a-mountain-array/
+ * Difficulty: Medium
+ *
+ * You are given an integer mountain array arr of length n where the values increase to a peak
+ * element and then decrease.
+ *
+ * Return the index of the peak element.
+ *
+ * Your task is to solve it in O(log(n)) time complexity.
+ */
+
+/**
+ * @param {number[]} arr
+ * @return {number}
+ */
+var peakIndexInMountainArray = function(arr) {
+  let left = 0;
+  let right = arr.length - 1;
+
+  while (left < right) {
+    const middle = Math.floor((left + right) / 2);
+
+    if (arr[middle] > arr[middle + 1]) {
+      right = middle;
+    } else {
+      left = middle + 1;
+    }
+  }
+
+  return left;
+};