用户缓存解决递归在计算菲波拉契数列时的噩梦

用户缓存解决递归在计算菲波拉契数列时的噩梦
?php
function feibolaqi($v) {
    static $cache = array();
    if (isset($cache[$v])) return $cache[$v];
    if ($v  1) throw new Exception('错误');
    if ($v = 2) return 1;
    $result = feibolaqi($v - 1) + feibolaqi($v - 2);
    $cache[$v] = $result;
    return $result;
}
$start = gettimeofday(true);
echo feibolaqi(45) . '';
echo '耗时 ' . (gettimeofday(true) - $start);
?>