What is the functionality of the following piece of code? public Object…
2025
What is the functionality of the following piece of code?
public Object delete_key()
{
if(count == 0)
{
System.out.println("Q is empty");
System.exit(0);
}
else
{
Node cur = head.getNext();
Node dup = cur.getNext();
Object e = cur.getEle();
head.setNext(dup);
count--;
return e;
}
}
- A.
Delete the second element in the list
- B.
Return but not delete the second element in the list
- C.
Delete the first element in the list
- D.
Return but not delete the first element in the list
Show answer & explanation
Correct answer: C
Concept
In a linked-list ADT built with a sentinel (header) node, head itself never stores a data value: head.getNext() is the pointer to the first real data node. A node is removed from a singly linked list by having the pointer immediately before it reassigned to skip over it, unlinking it from the chain without touching the node itself.
Step-by-step trace
cur = head.getNext() makes cur reference the first data node in the list (the node right after the sentinel head).
dup = cur.getNext() makes dup reference the node that follows cur (one hop further from head).
e = cur.getEle() reads the value stored in cur before any pointer changes happen.
head.setNext(dup) reassigns head's next pointer from cur to dup, so cur is bypassed and is no longer reachable by following the chain from head.
count-- lowers the element count by one, consistent with cur having been unlinked.
return e sends back the value that was stored in cur, the node that was just removed.
Cross-check
Because head is a sentinel and its immediate successor is always the first data element, redirecting head's next pointer around cur removes exactly the first element while the rest of the chain (starting at dup) stays intact. Since e was read from cur before the pointer change, the code both deletes and returns the value of the first element in the list.