12. 三数之和

<?php
class Solution {
    public function threeSum($nums) {
        if (!$nums) return [];
        sort($nums);
        $ret = [];
        $count = count($nums);
        for ($i = 0; $i < $count - 2; $i++) {
            echo $i. '';
            if ($i > 0 && $nums[$i] == $nums[$i - 1]) continue;
            $left = $i + 1;
            $right = $count - 1;
            $need = 0 - $nums[$i];
            while($left < $right) {
                if ($nums[$left] + $nums[$right] == $need) {
                    array_push($ret, [$nums[$i], $nums[$left], $nums[$right]]);
                    while($left < $right && $nums[$left] == $nums[$left + 1]) $left++;
                    while($left < $right && $nums[$right] == $nums[$right - 1]) $right--;
                    $left++;
                    $right--;
                } else if ($nums[$left] + $nums[$right] > $need) {
                    $right--;
                } else {
                    $left++;
                }
            }
        }
        return $ret;
    }
}
$nums = [-1, 1, 0, -1, 2, -4, 5, 6, -11];
$cls = new Solution();
$r = $cls->threeSum($nums);
print_r($r);