从链表中删除偶数在尾节点上不起作用？

Question

void deleteEven() {
        boolean con = false;
        Node add;
        Node move;
        move = head;
        if (move.data % 2 == 0) {
            head = move.next;
            con = true;
        }
        add = move;
        move = move.next;
        while (move != null) {
            if (move.data % 2 == 0 ) {
                add.next = move.next;
                con = true;
            }
            add = move;
            move = move.next;
        }
        if (!con)
            System.out.println("No even numbers in list");
    }

It works for every node except the tail. if linked list is [5,4,3,2,2] the result is [5,3,2] How to fix that?

Answer 1

The problem is not with the tail node. The problem is with two even nodes in a row irrespective of where they are in the list. When the current node is even you are moving your pointer to the previous node ( add ) to the current node even though you have just removed it. For the second even node your add.next = move.next statement changes next for the node you have just removed.

The simplest solution is to only move add if the node is not even:

if (move.data % 2 == 1) {
    add.next = move.next;
    con = true;
} else {
    add = move.next;
}

You could simplify your code quite a bit by getting rid of add altogether and just looking one node ahead of move :

while (move.next != null) {
    if (move.next.data % 2 == 0) {
        move.next = move.next.next;
        con = true;
    } else {
        move = move.next;
    }
}

And a programming tip for you: have several test cases before trying to diagnose a problem. I have found it's very easy to jump to an incorrect conclusion based on a small number of test cases and often expanding the range will make the problem clearer. That is one of the (many) reasons that test driven development works as well as it does.

Answer 2

Let's create service Node for attaching other nodes.

Then loop through the list and copy the references in a new list (new Node are not created):

void deleteEven() {
    Node tmpHead = new Node(0, null);
    Node tmpCopy = tmpHead;
    Node tmp = head;
    while (tmp != null) {
        if (tmp.data % 2 == 1) {
            tmpCopy.next = tmp;
            tmpCopy = tmpCopy.next;
        }
        tmp = tmp.next;
    }
    tmpCopy.next = null;
    head = tmpHead.next;
}

Suppose what Node is:

class Node {
    int data;
    Node next;

    public Node(int data, Node next) {
        this.data = data;
        this.next = next;
    }
}