Solution.php

class Solution {
    /**
     * @param int[] $nums
     * @param int $target
     * @return int
     */

    function threeSumClosest($nums, $target) {
        $n = count($nums);
        $closestSum = $nums[0] + $nums[1] + $nums[2];
        $minDiff = abs($closestSum - $target);

        sort($nums);

        for ($i = 0; $i < $n - 2; $i++) {

            $left = $i + 1;
            $right = $n - 1;

            while ($left < $right) {
                $sum = $nums[$i] + $nums[$left] + $nums[$right];
                $diff = abs($sum - $target);

                if ($diff < $minDiff) {
                    $minDiff = $diff;
                    $closestSum = $sum;
                } elseif ($sum < $target) {
                    $left++;
                } elseif ($sum > $target) {
                    $right--;
                } else {
                    return $sum;
                }
            }
        }

        return $closestSum;
    }
}