Add solution #1191

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,174 LeetCode solutions in JavaScript
+# 1,175 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -923,6 +923,7 @@
 1187|[Make Array Strictly Increasing](./solutions/1187-make-array-strictly-increasing.js)|Hard|
 1189|[Maximum Number of Balloons](./solutions/1189-maximum-number-of-balloons.js)|Easy|
 1190|[Reverse Substrings Between Each Pair of Parentheses](./solutions/1190-reverse-substrings-between-each-pair-of-parentheses.js)|Medium|
+1191|[K-Concatenation Maximum Sum](./solutions/1191-k-concatenation-maximum-sum.js)|Medium|
 1200|[Minimum Absolute Difference](./solutions/1200-minimum-absolute-difference.js)|Easy|
 1206|[Design Skiplist](./solutions/1206-design-skiplist.js)|Hard|
 1207|[Unique Number of Occurrences](./solutions/1207-unique-number-of-occurrences.js)|Easy|

solutions/1191-k-concatenation-maximum-sum.js

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+/**
+ * 1191. K-Concatenation Maximum Sum
+ * https://leetcode.com/problems/k-concatenation-maximum-sum/
+ * Difficulty: Medium
+ *
+ * Given an integer array arr and an integer k, modify the array by repeating it k times.
+ *
+ * For example, if arr = [1, 2] and k = 3 then the modified array will be [1, 2, 1, 2, 1, 2].
+ *
+ * Return the maximum sub-array sum in the modified array. Note that the length of the sub-array
+ * can be 0 and its sum in that case is 0.
+ *
+ * As the answer can be very large, return the answer modulo 109 + 7.
+ */
+
+/**
+ * @param {number[]} arr
+ * @param {number} k
+ * @return {number}
+ */
+var kConcatenationMaxSum = function(arr, k) {
+  const MOD = 1e9 + 7;
+  const arraySum = arr.reduce((sum, num) => sum + num, 0);
+  const maxSingle = helper(arr);
+
+  if (k === 1) return maxSingle;
+
+  const doubleArray = [...arr, ...arr];
+  const maxDouble = helper(doubleArray);
+
+  if (arraySum > 0) {
+    return Number((BigInt(maxDouble) + BigInt(arraySum) * BigInt(k - 2)) % BigInt(MOD));
+  }
+
+  return maxDouble;
+};
+
+function helper(arr) {
+  let maxSoFar = 0;
+  let maxEndingHere = 0;
+
+  for (const num of arr) {
+    maxEndingHere = Math.max(0, maxEndingHere + num);
+    maxSoFar = Math.max(maxSoFar, maxEndingHere);
+  }
+
+  return maxSoFar;
+}