How Do I Print the values in a recursive Program in Java?

问题

I am trying to use a recursive program to print out a sequence that starts at one value, goes to a max, then back down to the original value. The program can't use static or global variables, or use an array.

Ex: f(5,10) prints 5,6,7,8,9,10,9,8,7,6,5

I think I have the concept down, at least I think I do, but I can't figure out how to print the variable from the recursive method to print the sequence.
Here is my program:

 public class recursive {

     public static int f(int a, int b) {
         System.out.print(a);   
         if (a == b) return a;
         else return a + f(a + 1, b) + a;

     public static void main(String[] args) {
         f(2, 5);
     }

 }

Do I need to Change the program to be able to print? I am fairly certain my concept is correct, I just can't print it. Please help!!!!

回答1:

If you must print inside the recursive function, just print instead of returning..

public static void f(int a, int b) {
    if (a == b) {
        System.out.print(a);
    }
    else {
        System.out.print(a + ",");
        f(a+1,b);
        System.out.print("," + a);
    }
}

回答2:

You can think of your output as a nested series of outputs. For instance, with f(5, 10), you should print a 5, then a comma, print f(6, 10), then print a comma and another 5. You just need to then identify and deal with the base case (where you don't recurse) and you will be done.

回答3:

If you can't use an array, that main(String []args) is going to be a problem ;)

What you want to do is:

boilerplate boilerplate void recursive(num, max) {
    System.out.print(num)

    if (number < max) {
        System.out.print(",");
        recursive(+1, max);
    }

    System.out.print(num)
}

boilerplate boilerplate main(String[] args) {
   recursive(1, 10);
}

Disclaimer: it's been about 15 years since I did java, so there's probably something very wrong with this -- apart from the "boilerplate" stuff ;)

回答4:

public class recursive {
    public static void f(int a, int b) {
        if (a == b) {
            System.out.print(a);
        } else {
            System.out.print(a + ",");
            f(a + 1, b);
            System.out.print("," + a);
        }
    }

    public static void main(String[] args) {
        f(2, 5);
    }
}

回答5:

public static void f(int a, int b) {
    if(a != b) {
        System.out.print(a + ",");
        if(a < b) {
            f(a + 1, b);
        } else {
            f(a - 1, b);
        }
        System.out.print("," + a);
    } else {
        System.out.print(a);
    }
}

public static void main(String[] args) {
    f(2, 5); //2,3,4,5,4,3,2
    System.out.println();
    f(5, 2); //5,4,3,2,3,4,5
}

There were a few problems with your code:

If a is greater than b, the code would continue to execute until you get a StackOverflowError.
When a and b are not equal, you're returning an integer, rather than a string.
Printing a + f(a + 1, b) + a will cause the wrong output to be printed because you're calling a print function inside of a print function.

来源：https://stackoverflow.com/questions/19236980/how-do-i-print-the-values-in-a-recursive-program-in-java

标签

java

recursion