PHP 电话号码的字母组合算法输出

<?php

function mobileNumToAlphabet(array $mobileNumA)
{
    $mobileAlphabet = array(
        '2' => array('a', 'b', 'c'),
        '3' => array('d', 'e', 'f'),
        '4' => array('g', 'h', 'i'),
        '5' => array('j', 'k', 'l'),
        '6' => array('m', 'n', 'o'),
        '7' => array('p', 'q', 'r', 's'),
        '8' => array('t', 'u', 'v'),
        '9' => array('w', 'x', 'y', 'z'),
    );
    $finish = array();
    // 如果数字不在
    $i = 0; // 深度
    foreach ($mobileNumA as $key => $value) {
        if (empty($mobileAlphabet[$value])) {
            unset($mobileNumA[$key]);
            continue;
        }

        if (empty($finish)) {
            $finish = $mobileAlphabet[$value];
            continue;
        }
        $i++;
        while (!empty($finish)) {
            $popStr = array_shift($finish);
            // 判断深度
            if (strlen($popStr) != $i) {
                array_unshift($finish, $popStr);
                break;
            }

            foreach ($mobileAlphabet[$value] as $alphabet) {
                $str = $popStr . $alphabet;
                array_push($finish, $str);
            }
        }
    }

    echo json_encode($finish, true);
}

mobileNumToAlphabet(array(2,3));

输出

["ad","ae","af","bd","be","bf","cd","ce","cf"]