Add solution #3208

Author: JoshCrozier

README.md

@@ -820,6 +820,7 @@
 3151|[Special Array I](./3151-special-array-i.js)|Easy|
 3160|[Find the Number of Distinct Colors Among the Balls](./3160-find-the-number-of-distinct-colors-among-the-balls.js)|Medium|
 3174|[Clear Digits](./3174-clear-digits.js)|Easy|
+3208|[Alternating Groups II](./3208-alternating-groups-ii.js)|Medium|
 3223|[Minimum Length of String After Operations](./3223-minimum-length-of-string-after-operations.js)|Medium|
 3392|[Count Subarrays of Length Three With a Condition](./3392-count-subarrays-of-length-three-with-a-condition.js)|Easy|
 3396|[Minimum Number of Operations to Make Elements in Array Distinct](./3396-minimum-number-of-operations-to-make-elements-in-array-distinct.js)|Easy|

solutions/3208-alternating-groups-ii.js

@@ -0,0 +1,46 @@
+/**
+ * 3208. Alternating Groups II
+ * https://leetcode.com/problems/alternating-groups-ii/
+ * Difficulty: Medium
+ *
+ * There is a circle of red and blue tiles. You are given an array of integers colors and
+ * an integer k. The color of tile i is represented by colors[i]:
+ * - colors[i] == 0 means that tile i is red.
+ *  -colors[i] == 1 means that tile i is blue.
+ *
+ * An alternating group is every k contiguous tiles in the circle with alternating colors
+ * (each tile in the group except the first and last one has a different color from its
+ * left and right tiles).
+ *
+ * Return the number of alternating groups.
+ *
+ * Note that since colors represents a circle, the first and the last tiles are considered
+ * to be next to each other.
+ */
+
+/**
+ * @param {number[]} colors
+ * @param {number} k
+ * @return {number}
+ */
+var numberOfAlternatingGroups = function(colors, k) {
+  const extended = colors.concat(colors.slice(0, k - 1));
+  let result = 0;
+  let invalid = 0;
+
+  for (let i = 1; i < k; i++) {
+    if (extended[i] === extended[i - 1]) {
+      invalid++;
+    }
+  }
+  if (invalid === 0) {
+    result++;
+  }
+  for (let i = 1; i < colors.length; i++) {
+    if (extended[i] === extended[i - 1]) invalid--;
+    if (extended[i + k - 1] === extended[i + k - 2]) invalid++;
+    if (invalid === 0) result++;
+  }
+
+  return result;
+};