<?php
mb_language('Japanese');
mb_internal_encoding('UTF-8');

class Zundoko {

    const ZUNDOCO_PHRASE = 'ズンズンズンズンドコ';

    public function kiyoshi(){
        $zundokoList = ["ズン", "ドコ"];
        $cache = "";
        do {
            $choice = $zundokoList[mt_rand(0, 1)];
            echo $choice;

            $cache .= $choice;
            $generated = mb_substr($cache, mb_strlen(self::ZUNDOCO_PHRASE) * -1);
        } while (strcmp(self::ZUNDOCO_PHRASE,$generated));
        echo "キ・ヨ・シ！";
    }

}

$zun = new Zundoko();
$zun->kiyoshi();