How does 1 2 3 come at the end?

Vikki Nayyar :

In this program, if the user enters the number 3, the o/p will be 3 2 1 1 2 3 , I understood how 3 2 1 came, but I didn't understand how 1 2 3 came at the end.

class GFG{ 
static void printFun(int test) 
{ 
    if (test < 1) 
        return; 
    else
    { 
        System.out.printf("%d ",test); 
        printFun(test-1); // statement 2 
        System.out.printf("%d ",test); 
        return; 
    } 
} 

public static void main(String[] args) 
{ 
    int test = 3; 
    printFun(test); 
} 
}

Sweeper :

One way to trace through recursive functions is by expanding every recursive call, like a math expression.

First we start with

printFun(3)

That expands to:

print(3) // I have shortened System.out.printf here to just "print" to remove the noise
printFun(2)
print(3)

We still have a recursive call (printFun(2)), so let's expand that.

print(3)
print(2)
printFun(1)
print(2)
print(3)

Continue expanding:

print(3)
print(2)
print(1)
printFun(0)
print(1)
print(2)
print(3)

And one last time (since printFun(0) doesn't do anything, we just remove it):

print(3)
print(2)
print(1)
print(1)
print(2)
print(3)

Oh look! That will produce the output 3 2 1 1 2 3!