Why are these functions incorrect and how can I change it to pass the tests with recursion and no lists. public class Bl

[answerhappygod]

Why are these functions incorrect and how can I change
it to pass the tests with recursion and no lists.
public class Block {
public int id; // Number
public int rank; // position in the Chain
public Block next;
// attributes to be added
public int size;
public Block(int id, int rank) {






this.id = id;
this.rank = rank;
this.next = null;
// attributes to be
added

}







public Block(int id, int rank, Block next)
{






this.id = id;
this.rank = rank;
this.next = next;
// attributes to be
added

}
// Additional constructors may be added
// DO NOT MODIFY
public String toString() {






String str = "(" + id + ", "
+ rank + ")";
if (this.next == null)
{
return
str;
}
return str + " -> " +
next.toString();
}
* @return true if the chain starting at the current node
is a valid Collatz
* chain and false
otherwise. For a chain to be valid, it needs to
* follow the 3n+1
rule but not necessarily have a valid rank. The fast
* collatz chain
should be treated as invalid.
*/






public boolean isValid() {

if(this.next == null) {
return
true;
}
else
if(this.id % 2 == 0 && this.id / 2 == this.next.id) {
return
next.isValid();
}
else
if(this.id % 2 == 1 && this.id * 3 + 1 == this.next.id)
{
return
next.isValid();
}
else
{
return
false;
}
}



/**






* IMPORTANT: Even thought this method is in the
Block class, it may be harder
* than most in the Chain class.
*
* @return true if the chain starting at the
current node is either a valid
* Collatz chain or
a fast Collatz chain. In this question, you also
* need to ensure
that the rank is valid. A valid rank starts at 1 and
* increases with
one.
*/






public boolean isValidAdvanced() {

if(next == null) {
return
false;
}
else
if(next.id % 2 == 0 && next.id / 2 == id &&
next.rank == rank + 1) {
return
isValidAdvanced();
}
else
if(next.id % 2 == 1 && next.id * 3 + 1 == id &&
next.rank == rank + 1) {
return
isValidAdvanced();
}
else
{
return
false;
}

}





}