Question

# Give the output of the following program. Then explain what the foo() method does, in general,...

Give the output of the following program. Then explain what the foo() method does, in general, for a given input. Is foo() a tail-recursive method? Why or why not?

class SomeThing {

public static void main(String args[]) {

System.out.println(foo(6));

}

private static int foo(int input) {

if (input <= 0) {

throw new RuntimeException("invalid input");

}

else if (input == 1) {

return 1;

}

else if (input % 2 == 0) {

return foo(input - 1);

}

else {

return input * foo(input-2);

}

}

}

OUTPUT:

15

Explaination:

5 * 3 * 1 = 15

The above program gives the multiplication of all odd numbers less than the number passed while initially calling the function.

Tracing:

Step 1: foo(6)

Step 2: foo(6-1) [since (6%2) == 0, so, this function is going to call recursively passing input-1]

Step 3: 5 * foo(5-2) [Here, else part runs, It is going to multiply the input with foo(input -2)]

Step 4: 5 * 3 * foo(1) [Here, foo(1) is going to return 1]

Step 5: 5 * 3 * 1 [The final value is returned]

Step 6: 15 [Output]

This function is not a tail-recursive function.

```The function is not tail recursive because the value returned by foo(input-2) from Step3 is used in computation in the further steps.```