LeftAndRightSumDifferences.php

<?php

namespace App;

/**
 * Left and Right Sum Differences
 *
 * Given a 0-indexed integer array nums, find a 0-indexed integer array answer where:
 * - answer.length == nums.length.
 * - answer[i] = |leftSum[i] - rightSum[i]|.
 * Where:
 * - leftSum[i] is the sum of elements to the left of the index i in the array nums. If there is no such element,
 * leftSum[i] = 0.
 * - rightSum[i] is the sum of elements to the right of the index i in the array nums. If there is no such element,
 * rightSum[i] = 0.
 * Return the array answer.
 *
 * Example 1:
 * Input: nums = [10,4,8,3]
 * Output: [15,1,11,22]
 * Explanation: The array leftSum is [0,10,14,22] and the array rightSum is [15,11,3,0].
 * The array answer is [|0 - 15|,|10 - 11|,|14 - 3|,|22 - 0|] = [15,1,11,22].
 *
 * Example 2:
 * Input: nums = [1]
 * Output: [0]
 * Explanation: The array leftSum is [0] and the array rightSum is [0].
 * The array answer is [|0 - 0|] = [0].
 *
 * https://leetcode.com/problems/left-and-right-sum-differences
 */
class LeftAndRightSumDifferences
{
    /**
     * @param int[] $nums
     * @return int[]
     */
    public function leftRightDifference(array $nums): array
    {
        $leftSum = [0];
        $rightSum = [0];
        $sum = 0;
        foreach ($nums as $num) {
            $sum += $num;
            $leftSum[] = $sum;
        }
        $sum = 0;
        foreach (array_reverse($nums) as $num) {
            $sum += $num;
            $rightSum[] = $sum;
        }
        $rightSum = array_reverse($rightSum);
        $answer = [];
        for ($i = 0, $iMax = count($nums); $i < $iMax; $i++) {
            $answer[] = abs($leftSum[$i] - $rightSum[$i + 1]);
        }
        return $answer;
    }
}