Add solution #540

Author: JoshCrozier

README.md

@@ -430,6 +430,7 @@
 537|[Complex Number Multiplication](./0537-complex-number-multiplication.js)|Medium|
 538|[Convert BST to Greater Tree](./0538-convert-bst-to-greater-tree.js)|Medium|
 539|[Minimum Time Difference](./0539-minimum-time-difference.js)|Medium|
+540|[Single Element in a Sorted Array](./0540-single-element-in-a-sorted-array.js)|Medium|
 541|[Reverse String II](./0541-reverse-string-ii.js)|Easy|
 542|[01 Matrix](./0542-01-matrix.js)|Medium|
 543|[Diameter of Binary Tree](./0543-diameter-of-binary-tree.js)|Easy|

solutions/0540-single-element-in-a-sorted-array.js

@@ -0,0 +1,33 @@
+/**
+ * 540. Single Element in a Sorted Array
+ * https://leetcode.com/problems/single-element-in-a-sorted-array/
+ * Difficulty: Medium
+ *
+ * You are given a sorted array consisting of only integers where every element appears
+ * exactly twice, except for one element which appears exactly once.
+ *
+ * Return the single element that appears only once.
+ *
+ * Your solution must run in O(log n) time and O(1) space.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var singleNonDuplicate = function(nums) {
+  let left = 0;
+  let right = nums.length - 1;
+
+  while (left < right) {
+    let middle = left + Math.floor((right - left) / 2);
+    middle = middle - (middle % 2);
+    if (nums[middle] === nums[middle + 1]) {
+      left = middle + 2;
+    } else {
+      right = middle;
+    }
+  }
+
+  return nums[left];
+};