Add solution #523

Author: JoshCrozier

README.md

@@ -419,6 +419,7 @@
 520|[Detect Capital](./0520-detect-capital.js)|Easy|
 521|[Longest Uncommon Subsequence I](./0521-longest-uncommon-subsequence-i.js)|Easy|
 522|[Longest Uncommon Subsequence II](./0522-longest-uncommon-subsequence-ii.js)|Medium|
+523|[Continuous Subarray Sum](./0523-continuous-subarray-sum.js)|Medium|
 530|[Minimum Absolute Difference in BST](./0530-minimum-absolute-difference-in-bst.js)|Easy|
 541|[Reverse String II](./0541-reverse-string-ii.js)|Easy|
 542|[01 Matrix](./0542-01-matrix.js)|Medium|

solutions/0523-continuous-subarray-sum.js

@@ -0,0 +1,43 @@
+/**
+ * 523. Continuous Subarray Sum
+ * https://leetcode.com/problems/continuous-subarray-sum/
+ * Difficulty: Medium
+ *
+ * Given an integer array nums and an integer k, return true if nums has a good subarray
+ * or false otherwise.
+ *
+ * A good subarray is a subarray where:
+ * - its length is at least two, and
+ * - the sum of the elements of the subarray is a multiple of k.
+ *
+ * Note that:
+ * - A subarray is a contiguous part of the array.
+ * - An integer x is a multiple of k if there exists an integer n such that x = n * k.
+ *   0 is always a multiple of k.
+ */
+
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {boolean}
+ */
+var checkSubarraySum = function(nums, k) {
+  const map = new Map([[0, -1]]);
+
+  for (let i = 0, sum = 0; i < nums.length; i++) {
+    sum += nums[i];
+    if (k !== 0) {
+      sum = sum % k;
+    }
+
+    if (map.has(sum)) {
+      if (i - map.get(sum) >= 2) {
+        return true;
+      }
+    } else {
+      map.set(sum, i);
+    }
+  }
+
+  return false;
+};