Created
October 22, 2012 17:25
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| add a method set(int n, Object o) which replaces the nth element in the list |
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| public class Assignment { | |
| public static void main(String[] args) { | |
| LinkedList list = new LinkedList(); | |
| for(int i = 4; i > 0; i--) { | |
| list.addFirst(i); | |
| } | |
| list.print(); | |
| System.out.println("The size is: " + list.size() + "."); | |
| list.set(2, 66); | |
| list.print(); | |
| } | |
| } |
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| public class LinkedList { | |
| private class ListElement { | |
| private Object el1; | |
| private ListElement el2; | |
| public ListElement(Object el, ListElement nextElement) { | |
| el1 = el; | |
| el2 = nextElement; | |
| } | |
| public ListElement(Object el) { | |
| this(el,null); | |
| } | |
| public Object first() { | |
| return el1; | |
| } | |
| public ListElement rest() { | |
| return el2; | |
| } | |
| public void setFirst(Object value) { | |
| el1 = value; | |
| } | |
| public void setRest(ListElement value) { | |
| el2 = value; | |
| } | |
| } | |
| private ListElement head; | |
| private int count; | |
| public LinkedList() { | |
| head = null; | |
| } | |
| public void addFirst(Object o) { | |
| head = new ListElement(o,head); | |
| count++; | |
| } | |
| public Object getFirst() { | |
| return head.first(); | |
| } | |
| public Object get(int n) { | |
| ListElement d = head; | |
| while(n>0) | |
| { | |
| d = d.rest(); | |
| n--; | |
| } | |
| return d.first(); | |
| } | |
| public void print() { | |
| System.out.print("("); | |
| ListElement d = head; | |
| while(d != null) | |
| { | |
| System.out.print(d.first().toString() + " "); | |
| d = d.rest(); | |
| } | |
| System.out.println(")"); | |
| } | |
| public int size() { | |
| return count; | |
| } | |
| public void set(int n, Object o) { | |
| // first, try to find n-1 and n+1; let's call them nMin and nPlus | |
| ListElement nMin = null; | |
| ListElement nPlus; | |
| if (n > 0) { | |
| // if we're not setting element with index 0, we can run through the linked list | |
| nMin = head; | |
| while (n-1 < 0) { | |
| nMin = nMin.rest(); | |
| n--; | |
| } | |
| // and we can use n-1 to find n+1 | |
| nPlus = nMin.rest().rest() | |
| } else { | |
| // Otherwise, n+1 is really just element with index 1, or head.rest() | |
| // in this case, nMin doesn't exist, so we let it be 0 | |
| nPlus = head.rest(); | |
| } | |
| // turn this element into a ListElement and make it point to n+1 | |
| // because we're going to insert this element between n-1 and n+1 | |
| ListElement thisObject = new ListElement(o, nPlus); | |
| // if nMin is null, that means we're making a new head, so just assing the new object to the head | |
| if (nMin == null) { | |
| head = thisObject; | |
| } else { | |
| // otherwise, make n-1 point to this element | |
| nMin.setRest(thisObject); | |
| } | |
| // and we're done. obviously, this could fail in a number of ways, most likely nullpointer exceptions because we're not sanitising the "n" parameter at all. but whatever. | |
| } | |
| } |
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