合并2个链表

Question

I'm trying merge the 2 linked lists together, list1 and list2. In list2 you have an item that isn't available in list1 which is keyboard, also quantity of mouse has been changed, new quantity of mouse is going to be 3 because in list1 there was 1 mouse quantity and in list2 there are 3. So essentially you're going to have a new linked list called, let's say list3. list3 will combine the contents of list1 and list2 toghether, like the item keyboard which was in list2 but not list1 and also the new quantity of mouse.

 import java.util.LinkedList; import java.util.ListIterator; public class TestLinkedList extends MyLinkedList { public static void main(String[] args) { LinkedList < String > list1 = new LinkedList < > (); Demo demo = new Demo(); String case1 = demo.setNameandQty(1, "Case"); String monitor1 = demo.setNameandQty(3, "Monitor"); String mouse1 = demo.setNameandQty(1, "Mouse"); String ram1 = demo.setNameandQty(2, "RAM"); String ssd1 = demo.setNameandQty(4, "SSD"); int cm = 2; list1.add(case1); list1.add(monitor1); list1.add(mouse1); list1.add(ram1); list1.add(ssd1); System.out.println("Shopping List 1"); ListIterator < String > it1 = list1.listIterator(); while (it1.hasNext()) { System.out.println(it1.next()); } list1.remove(3); System.out.println("\\nAfter deleting 4th item"); for (String s: list1) { System.out.println(s); } LinkedList < String > list2 = new LinkedList < > (); String keyboard2 = demo.setNameandQty(1, "Keyboard"); String mouse2 = demo.setNameandQty(2, "Mouse"); list2.add(keyboard2); list2.add(mouse2); System.out.println("\\nShopping list 2"); for (String s: list2) { System.out.println(s); } String holdMouse1q = ""; String holdMouse2q = ""; String getMouse1q = demo.getIntegers(mouse1, holdMouse1q); int mouse1q = Integer.parseInt(getMouse1q); String getMouse2q = demo.getIntegers(mouse2, holdMouse2q); int mouse2q = Integer.parseInt(getMouse2q); System.out.println("\\nMouse 1 quantity: " + mouse1q); System.out.println("Mouse 2 quantity: " + mouse2q); int totalMouseQ = mouse1q + mouse2q; // list1.addFirst("Flashdisks : 10"); // System.out.println("\\nAfter adding 10 flash disks"); // for (String s : list1) { // System.out.println(s); // } } } 

Answer 1

I'm not sure what the return value of method demo.setNameandQty() is. So I just assume the return value should be like <name>-<quality> , eg. "Mouse-2".

Below is my merge method, solve by sort the list of items:

private static List<String> merge(List<String> list1, List<String> list2){
Collections.sort(list1);
Collections.sort(list2);
//ensure list always has 1 element
list1.add(null);
list2.add(null);

List<String> list3 = new LinkedList<String>();

Iterator<String> l1 = list1.iterator();
Iterator<String> l2 = list2.iterator();

String item1 = l1.next();
String item2 = l2.next();
while(item1 != null && item2 != null){
    String name1 = getName(item1);
    String name2 = getName(item2);
    if(name1.compareTo(name2) < 0){
        list3.add(item1);
        item1 = l1.next();
    }
    else if(name1.compareTo(name2) > 0){
        list3.add(item2);
        item2 = l2.next();
    }
    else if(name1.compareTo(name2) == 0){
        //sum up the quality then add to the list
        int totalQty = getQuality(item1) + getQuality(item2);
        list3.add(name1 + "-" + totalQty);
        item1 = l1.next();
        item2 = l2.next();
    }
}

//add the rest of the list, in case one of two lists still has items
while(item1 != null){
    list3.add(item1);
    item1 = l2.next();
}
while(item2 != null){
    list3.add(item2);
    item2 = l2.next();
}

return list3;
}    
private static String getName(String s){
    return s.substring(0, s.indexOf('-'));
}
private static int getQuality(String s){
    return Integer.valueOf(s.substring(s.indexOf('-')+1));
}

One note here that this method would fail if you have duplicate item in one list, eg. {"Mouse-1","Mouse-2"}. To fix that, I think we better insure there is no duplicate item instead of making our merge method more complicated.