我正在做家庭作业，经过几天的努力，我无法弄清楚为什么，在我的mergeSort实现后，我的列表只包含我链接列表中的最后一个对象。它不输出我的整个链表，只输出最后一个对象。如何更改我的代码以阻止我的列表在一个对象后转动null。
请注意：虽然我称之为立方体，但我知道它们不是因为它们具有随机长度，宽度和高度。赋值指定它们被称为多维数据集，但具有这些随机数据字段。请忽略这一点。
public class SortingCubes {
public static void main(String[] args) {
System.out.println(" ");
System.out.println("-----MY LINKED LIST-----");
Cube headCubeLL = new Cube(); //Create head cube
int LLnum = 5; //Change number of linked list items desired here
for(int i = 0; i < LLnum; i++) {
headCubeLL.length = Math.random() * 99 + 1; //Create random L,W,H for each cube (between 1-100)
headCubeLL.width = Math.random() * 99 + 1;
headCubeLL.height = Math.random() * 99 + 1;
headCubeLL.next = null; //Sets end of list to null
if(headCubeLL.next == null) { //creates new cube until desired number is reached in the for loop
Cube curr = new Cube(headCubeLL.length, headCubeLL.width, headCubeLL.height);
headCubeLL = curr;
}
headCubeLL.next = null; //Sets last cube (next) to null to end the list.
System.out.println(headCubeLL.toString() + " "); //Print my Linked list until end
}
System.out.println(" ");
System.out.println("-----NEW LINKED LIST AFTER MERGE SORT METHOD IS IMPLEMENTED (Asending Order by Volume)-----");
long startTimeMergeSort = System.nanoTime();
mergeSort(headCubeLL);
long timeElapsedMergeSort = (System.nanoTime()- startTimeMergeSort);
printList(headCubeLL); //Method to print linked list
System.out.println("Objects in list " + count(headCubeLL));
long startTimeInsertionSort = System.nanoTime();
System.out.println(" ");
System.out.println("Time Record: ");
System.out.println("Time elapsed for Merge sort on a Linked List: " + timeElapsedMergeSort + " Nanos");
} //End of Main
public static void printList(Cube headCubeLL){
while(headCubeLL != null){
System.out.println(headCubeLL.toString() + " ");
headCubeLL = headCubeLL.next;
}
System.out.println();
}
public static int count(Cube head){
int count = 0;
while(head != null){
//System.out.println(head);
count++;
head = head.next;
}
return count;
}
public static Cube mergeSort(Cube headCubeLL) {
if(headCubeLL == null || headCubeLL.next == null) { //checking list is null
return headCubeLL;
}
int count = 0; //To count the total number of elements
Cube temp = headCubeLL; //Temporary head of list
while(temp != null) { //break up the list into two parts
count++; //while not empty, count one and move temp to temp.next to evaluate
temp = temp.next;
}
int middle = count/2; //create an integer called middle and divide the length of your list (count) by 2
Cube a = headCubeLL; //another temp head cube for 1st split list
Cube b = null; //another cube that is null
Cube temp2 = headCubeLL; //create another temp head cube for 2nd list
int countHalf = 0; //start at half 0 again
while(temp2 != null) { //while temp I have for 2nd list is not null....
countHalf++; //add count to get length of linked list
Cube theNext = temp2.next; //Create new cube that will be assigned to cube after head
if(countHalf == middle) { //once it reaches middle number
temp2.next = null; //end list (set head.next to null for list 2)
b = theNext; //Take my empty null cube and assign it to end with null.
}
temp2 = theNext; //Otherwise - move along and my temp head will be the temp head.next
}
//Now I have 2 parts, List a and List b.
Cube half1 = mergeSort(a); //Recursively call to sort each half
Cube half2 = mergeSort(b);
//Merge together
Cube merged = merge(half1, half2); //Call 2nd method to merge the 2 halves together
//System.out.println(merged.toString()); //Print the L,W,H and Volume of each cube in my array
return merged; //return merged list.
}
public static Cube merge(Cube a, Cube b) { //parameters are the 2 half's of the original list
Cube pt1 = a; //2 parts that I am going to merge as ascending lists according to volume
Cube pt2 = b;
Cube tempHead = new Cube(); //Temp head of my New list that cubes will be merged into
Cube ptNew = tempHead; //Temp Head for List my new list
while(pt1 != null || pt2 != null) { //While either list is not empty
if(pt1 == null) { //but if first is null
ptNew.next = new Cube(pt2.cubeVolume()); //create new cube for every cube volume
pt2 = pt2.next; //loop
}
else if(pt2 ==null){ //but if 2nd is null
ptNew.next = new Cube(pt1.cubeVolume()); //create new cube for every cube volume
pt1 = pt1.next; //loop
ptNew = ptNew.next; //move on by assigning moving to next cube creating when pt2 is == null
}
else {
if(pt1.cubeVolume() < pt2.cubeVolume()) { //moving while merging - comparing volumes of the head of each list
ptNew.next = new Cube(pt1.cubeVolume()); //When one is greater then new cube creating in new list and cube is placed accordingly
pt1 = pt1.next; //loop
ptNew = ptNew.next; //loop through new merged list for next comparison
}
else if(pt1.cubeVolume() == pt2.cubeVolume()) { //statement if the cubes volumes are equal
ptNew.next = new Cube(pt1.cubeVolume());
ptNew.next.next = new Cube(pt1.cubeVolume());
ptNew = ptNew.next.next;
pt1 = pt1.next; //place one next to the other
pt2 = pt2.next;
}
else {
ptNew.next = new Cube(pt2.cubeVolume()); //else made new cube in new list and place pt2 head
pt2 = pt2.next; //loop
ptNew = ptNew.next; //loop
}
}
}
return tempHead.next; //return new merged list
}
} //End of Class
我的立方体类:(所有正确仅供参考）
public class Cube {
double length;
double width;
double height;
Cube next = null;
public Cube() { //Default Constructor
}
public Cube(double volume) {
volume = this.cubeVolume();
}
public Cube(Double length, double width, double height) {
this.length = length;
this.width = width;
this.height = height;
this.next = next;
}
public String toString() { //Print into a String
return "CUBE Volume: (" + cubeVolume() + ") ----- CUBE Length: ("+ this.length +") ----- CUBE Width (" + this.width + ") ----- CUBE Height (" + this.height + ")";
}
//Set length
public void setLength(double length) {
this.length = length;
}
//Get length
public double getLength() {
return this.length;
}
//Set Width
public void setWidth(double width) {
this.width = width;
}
//Get Width
public double getWidth() {
return this.width;
}
//Set Height
public void setheight(double height) {
this.height = height;
}
//Set Height
public double setHeight() {
return this.height;
}
//Set Next
public void setNext(Cube next) {
this.next = next;
}
//Get Next
public Cube getNext() {
return this.next;
}
public double cubeVolume () {
double volume = (length*width*height);
//System.out.println("TEST: " + volume);
return volume;
}
} //End of Class
输出
-----MY LINKED LIST-----
CUBE Volume: (14550.645379921463) ----- CUBE Length: (19.526751823368887) ----- CUBE Width (54.77537177724803) ----- CUBE Height (13.604009167732666)
CUBE Volume: (1631.5144309742377) ----- CUBE Length: (40.72878317573845) ----- CUBE Width (22.07526604887876) ----- CUBE Height (1.8146109949933575)
CUBE Volume: (17837.576670179817) ----- CUBE Length: (4.606784797762423) ----- CUBE Width (78.5447210731351) ----- CUBE Height (49.29704940251802)
CUBE Volume: (113668.01972101796) ----- CUBE Length: (24.366242383656253) ----- CUBE Width (54.33809524521938) ----- CUBE Height (85.85099307890556)
CUBE Volume: (432771.5800393206) ----- CUBE Length: (83.95704403819472) ----- CUBE Width (56.0616051224998) ----- CUBE Height (91.94668276748753)
-----NEW LINKED LIST AFTER MERGE SORT METHOD IS IMPLEMENTED (Asending Order by Volume)-----
CUBE Volume: (432771.5800393206) ----- CUBE Length: (83.95704403819472) ----- CUBE Width (56.0616051224998) ----- CUBE Height (91.94668276748753)
Objects in list 1
Time Record:
Time elapsed for Merge sort on a Linked List: 11831 Nanos
答案 0 :(得分：1)
问题在于您的main方法，而不是您的排序方法。这个块
headCubeLL.next = null; //Sets end of list to null
if(headCubeLL.next == null) { //creates new cube until desired number is reached in the for loop
Cube curr = new Cube(headCubeLL.length, headCubeLL.width, headCubeLL.height);
headCubeLL = curr;
}
headCubeLL.next = null;
将始终进入if部分。您根本没有设置next的{{1}}字段。因此，当您将curr分配给curr时，您将丢失先前的headCubeLL值。这意味着列表中只有一个对象。每次创建新对象时都会丢弃该对象。
你需要
headCubeLL headCubeLL.next = null;后添加新行curr.setNext(headCubeLL);。这样，以前的curr将被记住，作为刚刚创建的新对象的headCubeLL元素。