0390-elimination-game.js

/**
 * 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;
};