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I see this algorithm in one answer, and now I have doubts Is a recursive function with two parameters, an integer array and a integer. The objective is to print the array but in the reverse order, I test it and it works! but I don't know why... Here is the function

public static void reverse(int[] a, int position) {
          // BASE
          if (position == a.length)  return;
          // RECURSIVE

          reverse(a, position + 1);

          System.out.println(a[position]);
        }

}

if the condition is true, the return doesn't mean that the program will end? and if it's false, the function will do the recursive call without printing the number, or not? Thanks!

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    Take a debugger and follow the flow. Commented Apr 15, 2013 at 21:15

3 Answers 3

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The return statement doesn't mean that the program will end. It means that this particular call of the method ends.

The next statement is the recursive call. It keeps calling itself with each possible position from 0 to the length of the array. So the first time that the code makes it past the recursive call is after the last recursive method returns and position is now at the end of the array. Then it prints the last character. It returns, and the previous recursive call, which has the previous position value, prints the next-to-last character, and so on, until the original call to the recursive method prints the first character, and then it's done.

E.g. for an array of length 3 {10, 11, 12}

reverse(a, 0)
    reverse(a, 1)
        reverse(a, 2)
            reverse(a, 3)
            base case; return
        print a[2] "12"
    print a[1] "11"
print a[0] "10"
done
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return is not an "exit " statement. return returns the program to where the method was called from and the next line is executed. System.exit(0) would end your program and halt all executions.

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The key concept behind this is, you need to understand how stacks work. Each call to a function is a stack, doesn't matter if it is calling from some other function or from itself.

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