<?php
$fun=function($n){$list=[1];while ($n--) {foreach ($list as $k => $v) {if($v%2==0){$list[]=1;//生一头小牛
            }if($v==5){unset($list[$k]);//到五岁了 牛死了continue;}$list[$k]++;//牛长大了一岁
        }}return count($list);//返回牛的数目
};
echo $fun(10);
exit();

<?php
$fun1 = function($n){$list = [1];while($n--){foreach($list as $k => $v){if($v%2 == 0){$list[] = 1;}if($v == 5){//unset($list[$k]);$list[$k] = array_pop($list);continue;}$list[$k]++;}}return count($list);
};echo $fun1(100);
exit();

<?php
$sum=get_cow_num(10);
var_dump($sum);
exit();function get_cow_num($n)
{$sum=1;for ($i=1; $i < $n; $i++){$sum = $i%2!=0 ? $sum*2 : $sum-peibona($i/2-1);//奇数年要翻倍 偶数年减去斐波那契数
    }return $sum;
}
function peibona($n)
{if($n<=0){return 0;}if($n<=2){return 1;}return peibona($n-1)+peibona($n-2);
}

<?php
set_time_limit(0);
$sum=get_cow_num(100);
var_dump($sum);
exit();function get_cow_num($n)
{$sum=1;for ($i=1; $i < $n; $i++){$sum = $i%2!=0 ? $sum*2 : $sum-peibona($i/2-1);//奇数年要翻倍 偶数年减去斐波那契数
    }return $sum;
}
function peibona($n)
{if($n<=0){return 0;}if($n<=2){return 1;}$array=array_fill(0,$n,0);$array[0]=0;$array[1]=1;$array[2]=1;for ($i=3; $i <= $n; $i++){$array[$i]=$array[$i-1]+$array[$i-2];}return $array[$n];
}

<?php
set_time_limit(0);
$sum=get_cow_num(100);
var_dump($sum);
exit();function get_cow_num($n)
{$sum=1;for ($i=1; $i < $n; $i++){$sum = $i%2!=0 ? $sum*2 : $sum-peibona($i/2-1,$n/2-1);//奇数年要翻倍 偶数年减去斐波那契数
    }return $sum;
}
function peibona($n,$total_num)
{static $array;if(!isset($array[$n])){if($n<=0){$array[$n]=0;}elseif($n<=2){$array[$n]=1;}else{$array=array_fill(0,$n,0);$array[0]=0;$array[1]=1;$array[2]=1;for ($i=3; $i <= $n; $i++){$array[$i]=$array[$i-1]+$array[$i-2];}}}return $array[$n];
}