SinglyLinkList

SinglyLinkList.java

class SinglyLinkList {
    private Node start;
    private Node end;
    private int size;

    // constructor
    public SinglyLinkList() {
        start = null;
        end = null;
        size = 0;
    }

    // append an element at beginning
    public void insertAtStart(int val) {
        Node nptr = new Node(val, null);
        size++;
        if (start == null) {
            start = nptr;
            end = start;
        } else {
            nptr.setNext(start);
            start = nptr;
        }
    }

    // append an element at end
    public void insertAtEnd(int val) {
        Node nptr = new Node(val, null);
        size++;
        if (start == null) {
            start = nptr;
            end = start;
        } else {
            end.setNext(nptr);
            end = nptr;
        }
    }

    // append an element at position
    public void insertAtPos(int val, int pos) {
        Node nptr = new Node(val, null);
        Node ptr = start;
        pos = pos - 1;
        for (int i = 1; i < size; i++) {
            if (i == pos) {
                Node tmp = ptr.getNext();
                ptr.setNext(nptr);
                nptr.setNext(tmp);
                break;
            }
            ptr = ptr.getNext();
        }
        size++;
    }

    // remove an element at position
    public void deleteAtPos(int pos) {
        if (pos == 1) {
            start = start.getNext();
            size--;
            return;
        }
        if (pos == size) {
            Node s = start;
            Node t = start;
            while (s != end) {
                t = s;
                s = s.getNext();
            }
            end = t;
            end.setNext(null);
            size--;
            return;
        }
        Node ptr = start;
        pos = pos - 1;
        for (int i = 1; i < size - 1; i++) {
            if (i == pos) {
                Node tmp = ptr.getNext();
                tmp = tmp.getNext();
                ptr.setNext(tmp);
                break;
            }
            ptr = ptr.getNext();
        }
        size--;
    }

    //    Remove the tail element
    public void removeLast() {
        if (end == null)
            return;
        else {
            if (start == end) {
                start = null;
                end = null;
            } else {
                Node previousToTail = start;
                while (previousToTail.getNext() != end) {
                    previousToTail = previousToTail.getNext();
                }
                end = previousToTail;
                end.setNext(null);
            }
        }
    }

    // Remove all element in the linked list that is great than a target value
    public int removeAllBasedOnInputValue(int val) {
        int counter = 0;
        Node current = start;

        //here we will go to the last node
        while (current.getNext() != null) {
            if (current.getData() > val) {
                /* Here, we need to verify 3 things:
                 * 1 - If it is the start;
                 * 2 - If it is the end; and
                 * 3 - If it is the body.
                 */

                /*1st verification -
                If the start is bigger than your value,
                then you just make your next node as "start",
                and make its previous as NULL.*/
                if (current == start) {
                    start = current.getNext();
                }/*2nd verification -
                If it is the last element,
                then you just make the next node of your previous be NULL.*/ else if (current.getNext() == null) {
                    end = null;
                }/*3rd verification -
                You will make the next of the previous as your current next;
                and the previous of the next as your current previous.
                In that way you will lose all the ways of reaching the current
                (which is greater than the value)*/ else {
                    current.next.next = current.next;
                }
                counter++;
            }
            current.setNext(current.getNext());
        }

        return counter;
    }

}

class Node {
    protected int data;
    protected Node next;

    //  Constructor
    public Node() {
        next = null;
        data = 0;
    }

    //  Constructor
    public Node(int d, Node n) {
        data = d;
        next = n;
    }

    // set link to next Node
    public void setNext(Node n) {
        next = n;
    }

    // set data to current Node
    public void setData(int d) {
        data = d;
    }

    // get link to next node
    public Node getNext() {
        return next;
    }

    //  get data from current Node
    public int getData() {
        return data;
    }
}