Add solution #390

Author: JoshCrozier

README.md

@@ -308,6 +308,7 @@
 387|[First Unique Character in a String](./0387-first-unique-character-in-a-string.js)|Easy|
 388|[Longest Absolute File Path](./0388-longest-absolute-file-path.js)|Medium|
 389|[Find the Difference](./0389-find-the-difference.js)|Easy|
+390|[Elimination Game](./0390-elimination-game.js)|Medium|
 392|[Is Subsequence](./0392-is-subsequence.js)|Easy|
 394|[Decode String](./0394-decode-string.js)|Medium|
 395|[Longest Substring with At Least K Repeating Characters](./0395-longest-substring-with-at-least-k-repeating-characters.js)|Medium|

solutions/0390-elimination-game.js

@@ -0,0 +1,35 @@
+/**
+ * 390. Elimination Game
+ * https://leetcode.com/problems/elimination-game/
+ * Difficulty: Medium
+ *
+ * You have a list arr of all integers in the range [1, n] sorted in a strictly increasing order.
+ * Apply the following algorithm on arr:
+ * - Starting from left to right, remove the first number and every other number afterward until
+ *   you reach the end of the list.
+ * - Repeat the previous step again, but this time from right to left, remove the rightmost number
+ *   and every other number from the remaining numbers.
+ * - Keep repeating the steps again, alternating left to right and right to left, until a single
+ *   number remains.
+ *
+ * Given the integer n, return the last number that remains in arr.
+ */
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var lastRemaining = function(n) {
+  let result = 1;
+
+  for (let isRemaining = true, count = n, step = 1; count > 1;) {
+    if (isRemaining || count % 2 === 1) {
+      result += step;
+    }
+    count = Math.floor(count / 2);
+    isRemaining = !isRemaining;
+    step *= 2;
+  }
+
+  return result;
+};