它的描述如下:
persistence(39) == 3 // because 3*9 = 27,2*7 = 14,1*4=4 // and 4 has only one digit persistence(999) == 4 // because 9*9*9 = 729,7*2*9 = 126,// 1*2*6 = 12,and finally 1*2 = 2 persistence(4) == 0 // because 4 is already a one-digit number
我只能这样做:
$array = str_split(39); foreach ($array as $key => $value) { echo $array[$key]*$array[$key+1]; }
接下来我很困惑
$array = str_split('999'); //Your string $j=0; //Counter for counting the number of iteration while (count($array)>1){ //When more than 2 indexes in array for($i=0;$i<count($array);$i++){ //Iterate through all permutations $array = array_product($array); //Multiplies all numbers in array $array = str_split($array); //Split the array up again $j++; //Increment counter(as literal as I can sound) } } echo $j; //Print out the number of times
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