如何使用递归来反转数字

Question

I want to send in the recursion only the number itself and not more variables!!!

so, I made a code that make the operation but I don't have the stop point.

the code:

public static int upsideDown (int number) {
    number += (number%10)*(Math.pow(10, String.valueOf(number).length()));
    number %= 10;
    return upsideDown (number);
}

Answer 1

You need to store the digit you are working with in a local variable instead of modifying number .

You need - instead of number %= 10 - to (integer) divide by 10 instead.

You need to multiply the previously stored digit by 10 raised to the power of string.length - 1 ; you need to add the result of this to the return value of the recursive call to upsideDown . Actually, a for loop over length - 1 , multiplying by 10 each time through the loop would be more efficient than using pow .

Exit code should simply be if (number == 0) return 0; at start of method.