<?php

namespace App;

/**
 * Apply Operations to an Array
 *
 * You are given a 0-indexed array nums of size n consisting of non-negative integers.
 * You need to apply n - 1 operations to this array where, in the ith operation (0-indexed), you will apply the
 * following on the ith element of nums:
 * - If nums[i] == nums[i + 1], then multiply nums[i] by 2 and set nums[i + 1] to 0. Otherwise, you skip this operation.
 * After performing all the operations, shift all the 0's to the end of the array.
 * - For example, the array [1,0,2,0,0,1] after shifting all its 0's to the end, is [1,2,1,0,0,0].
 * Return the resulting array. Note that the operations are applied sequentially, not all at once.
 *
 * Example 1:
 * Input: nums = [1,2,2,1,1,0]
 * Output: [1,4,2,0,0,0]
 * Explanation: We do the following operations:
 * - i = 0: nums[0] and nums[1] are not equal, so we skip this operation.
 * - i = 1: nums[1] and nums[2] are equal, we multiply nums[1] by 2 and change nums[2] to 0.
 * The array becomes [1,4,0,1,1,0].
 * - i = 2: nums[2] and nums[3] are not equal, so we skip this operation.
 * - i = 3: nums[3] and nums[4] are equal, we multiply nums[3] by 2 and change nums[4] to 0. The array becomes
 * [1,4,0,2,0,0].
 * - i = 4: nums[4] and nums[5] are equal, we multiply nums[4] by 2 and change nums[5] to 0. The array becomes
 * [1,4,0,2,0,0].
 * After that, we shift the 0's to the end, which gives the array [1,4,2,0,0,0].
 *
 * Example 2:
 * Input: nums = [0,1]
 * Output: [1,0]
 * Explanation: No operation can be applied, we just shift the 0 to the end.
 *
 * https://leetcode.com/problems/apply-operations-to-an-array
 */
class ApplyOperationsToArray
{
    /**
     * @param int[] $nums
     * @return int[]
     */
    public function applyOperations(array $nums): array
    {
        $length = count($nums);
        for ($i = 0; $i < $length - 1; $i++) {
            if ($nums[$i] === $nums[$i + 1]) {
                $nums[$i] *= 2;
                $nums[$i + 1] = 0;
            }
        }
        $result = [];
        foreach ($nums as $num) {
            if ($num !== 0) {
                $result[] = $num;
            }
        }
        for ($i = count($result); $i < $length; $i++) {
            $result[] = 0;
        }
        return $result;
    }
}
