13. 最接近的三数之和

<?php
class Solution {
    /**
     * nums = [-1, 2, 1, -4]
     * target = 1
     * closest = 2
     * @param $nums
     * @param $target
     * @return array|mixed
     */
    public function threeSumClosest($nums, $target) {
        if (!$nums) return [];
        sort($nums);
        $closest = $nums[0] + $nums[1] + $nums[2];
        for ($i = 0; $i < count($nums) - 2; $i++) {
            // 前后指针
            $left = $i + 1;
            $right = count($nums) - 1;
            while ($left < $right) {
                $sum = $nums[$i] + $nums[$left] + $nums[$right];
                if ($sum > $closest) {
                    $right--;
                } else {
                    $left++;
                }
                if (abs($sum - $target) < abs($closest - $target)) {
                    $closest = $sum;
                }
            }
        }
        return $closest;
    }
}
$nums = [-1, 2, 1, -4];
$cls = new Solution();
$r = $cls->threeSumClosest($nums, 1);
print_r($r);