Using Recursion to change digits in a number

Question

I made this method for an assignment in class. To count the number of '1's appearing in any given number. I would like to expand on this and learn how to take a number and if it is even number adds one to it. If it is an odd number subtract one from it using recursion and return that changed number.

public static int countOnes(int n){
    if(n < 0){
        return countOnes(n*-1);
    }
    if(n == 0){
        return 0;
    }
    if(n%10 == 1){
        return 1 + countOnes(n/10);
    }else 
        return countOnes(n/10);
}

0 would = 1 27 would = 36 so on. I would appreciate any help that is given.

There's no issue with the code that I posted I was just giving some reference as to why I decided to try and do what I am trying to do. @Eran — Anthony Perez
– Anthony Perez, Commented May 1, 2019 at 7:06
How is the number of 1s 36 in the number 27? I don't get it at all. Your description doesn't match the code at all. There's no odd-check in the code, only a '= 1 mod 10' check. — Mark Jeronimus
– Mark Jeronimus, Commented May 1, 2019 at 7:17
@MarkJeronimus the code is misleading. It has nothing to do with the problem OP is asking about, other than OP wrote it, it is recursive and OP is asking how to solve the problem recursively. — Andy Turner
– Andy Turner, Commented May 1, 2019 at 7:23

OldCurmudgeon · Accepted Answer · 2019-05-01 07:16:01Z

1

You quite often find that using private method in a recursive solution makes your code much clearer.

/**
 * Twiddles one digit.
 */
private static int twiddleDigit(int n) {
    return (n & 1) == 1 ? n - 1 : n + 1;
}

/**
 * Adds one to digits that are even, subtracts one from digits that are odd.
 */
public static int twiddleDigits(int n) {
    if (n < 10) return twiddleDigit(n);
    return twiddleDigits(n / 10) * 10 + twiddleDigit(n % 10);
}

answered May 1, 2019 at 7:16

OldCurmudgeon

66k18 gold badges126 silver badges220 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Using Recursion to change digits in a number

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related