Add solution #918

Author: JoshCrozier

README.md

@@ -488,6 +488,7 @@
 912|[Sort an Array](./0912-sort-an-array.js)|Medium|
 914|[X of a Kind in a Deck of Cards](./0914-x-of-a-kind-in-a-deck-of-cards.js)|Medium|
 916|[Word Subsets](./0916-word-subsets.js)|Medium|
+918|[Maximum Sum Circular Subarray](./0918-maximum-sum-circular-subarray.js)|Medium|
 922|[Sort Array By Parity II](./0922-sort-array-by-parity-ii.js)|Easy|
 925|[Long Pressed Name](./0925-long-pressed-name.js)|Easy|
 926|[Flip String to Monotone Increasing](./0926-flip-string-to-monotone-increasing.js)|Medium|

solutions/0918-maximum-sum-circular-subarray.js

@@ -0,0 +1,34 @@
+/**
+ * 918. Maximum Sum Circular Subarray
+ * https://leetcode.com/problems/maximum-sum-circular-subarray/
+ * Difficulty: Medium
+ *
+ * Given a circular integer array nums of length n, return the maximum possible sum of
+ * a non-empty subarray of nums.
+ *
+ * A circular array means the end of the array connects to the beginning of the array.
+ * Formally, the next element of nums[i] is nums[(i + 1) % n] and the previous element
+ * of nums[i] is nums[(i - 1 + n) % n].
+ *
+ * A subarray may only include each element of the fixed buffer nums at most once.
+ * Formally, for a subarray nums[i], nums[i + 1], ..., nums[j], there does not exist
+ * i <= k1, k2 <= j with k1 % n == k2 % n.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var maxSubarraySumCircular = function(nums) {
+  let [min, max, sum] = [nums[0], nums[0], nums[0]];
+
+  for (let i = 1, prevMin = nums[0], prevMax = nums[0]; i < nums.length; i++) {
+    prevMax = Math.max(nums[i], prevMax + nums[i]);
+    max = Math.max(max, prevMax);
+    prevMin = Math.min(nums[i], prevMin + nums[i]);
+    min = Math.min(min, prevMin);
+    sum += nums[i];
+  }
+
+  return max > 0 ? Math.max(max, sum - min) : max;
+};