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java-使用伪列表类
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我正在做一些家庭作业问题,而我陷入了困境.我很难理解交换列表中数据的最佳方法.
我应该使方法reverse(),它使用LinkedIntList类(如下).这是一个受限的列表类,因此我只能使用其中的内容.
关键是要列出项目清单
[1、2、3、4、5]
并扭转它们
[5,4,3,2,1]
我以为我的伪代码是
获取第一条数据并将其添加到列表中.
循环播放原始大小(因为更改)
并从0取出
然后在末尾的0,1位置添加当前片段.
对于这样的输入：
[1、8、19、4、17]
预期是这样的：
前面-> [17]-> [4]-> [19]-> [8]-> [1] /
我的代码得到这个：
前面-> [19]-> [4]-> [17]-> [8]-> [19]-> [1] /
不知道我在做什么错.
public void reverse(){
int x = this.size();
this.add(front.data);
for (int i = 0; i < x; i++){
this.remove(0);
this.add(this.size()-1, front.data);
}
}
// A LinkedIntList object can be used to store a list of integers.
public class LinkedIntList {
private ListNode front; // node holding first value in list (null if empty)
private String name = "front"; // string to print for front of list
// Constructs an empty list.
public LinkedIntList() {
front = null;
}
// Constructs a list containing the given elements.
// For quick initialization via Practice-It test cases.
public LinkedIntList(int... elements) {
this("front", elements);
}
public LinkedIntList(String name, int... elements) {
this.name = name;
if (elements.length > 0) {
front = new ListNode(elements[0]);
ListNode current = front;
for (int i = 1; i < elements.length; i++) {
current.next = new ListNode(elements[i]);
current = current.next;
}
}
}
// Constructs a list containing the given front node.
// For quick initialization via Practice-It ListNode test cases.
private LinkedIntList(String name, ListNode front) {
this.name = name;
this.front = front;
}
// Appends the given value to the end of the list.
public void add(int value) {
if (front == null) {
front = new ListNode(value, front);
} else {
ListNode current = front;
while (current.next != null) {
current = current.next;
}
current.next = new ListNode(value);
}
}
// Inserts the given value at the given index in the list.
// Precondition: 0 <= index <= size
public void add(int index, int value) {
if (index == 0) {
front = new ListNode(value, front);
} else {
ListNode current = front;
for (int i = 0; i < index - 1; i++) {
current = current.next;
}
current.next = new ListNode(value, current.next);
}
}
public boolean equals(Object o) {
if (o instanceof LinkedIntList) {
LinkedIntList other = (LinkedIntList) o;
return toString().equals(other.toString()); // hackish
} else {
return false;
}
}
// Returns the integer at the given index in the list.
// Precondition: 0 <= index < size
public int get(int index) {
ListNode current = front;
for (int i = 0; i < index; i++) {
current = current.next;
}
return current.data;
}
// Removes the value at the given index from the list.
// Precondition: 0 <= index < size
public void remove(int index) {
if (index == 0) {
front = front.next;
} else {
ListNode current = front;
for (int i = 0; i < index - 1; i++) {
current = current.next;
}
current.next = current.next.next;
}
}
// Returns the number of elements in the list.
public int size() {
int count = 0;
ListNode current = front;
while (current != null) {
count++;
current = current.next;
}
return count;
}
// Returns a text representation of the list, giving
// indications as to the nodes and link structure of the list.
// Detects student bugs where the student has inserted a cycle
// into the list.
public String toFormattedString() {
ListNode.clearCycleData();
String result = this.name;
ListNode current = front;
boolean cycle = false;
while (current != null) {
result += " -> [" + current.data + "]";
if (current.cycle) {
result += " (cycle!)";
cycle = true;
break;
}
current = current.__gotoNext();
}
if (!cycle) {
result += " /";
}
return result;
}
// Returns a text representation of the list.
public String toString() {
return toFormattedString();
}
// Returns a shorter, more "java.util.LinkedList"-like text representation of the list.
public String toStringShort() {
ListNode.clearCycleData();
String result = "[";
ListNode current = front;
boolean cycle = false;
while (current != null) {
if (result.length() > 1) {
result += ", ";
}
result += current.data;
if (current.cycle) {
result += " (cycle!)";
cycle = true;
break;
}
current = current.__gotoNext();
}
if (!cycle) {
result += "]";
}
return result;
}
// ListNode is a class for storing a single node of a linked list. This
// node class is for a list of integer values.
// Most of the icky code is related to the task of figuring out
// if the student has accidentally created a cycle by pointing a later part of the list back to an earlier part.
public static class ListNode {
private static final List<ListNode> ALL_NODES = new ArrayList<ListNode>();
public static void clearCycleData() {
for (ListNode node : ALL_NODES) {
node.visited = false;
node.cycle = false;
}
}
public int data; // data stored in this node
public ListNode next; // link to next node in the list
public boolean visited; // has this node been seen yet?
public boolean cycle; // is there a cycle at this node?
// post: constructs a node with data 0 and null link
public ListNode() {
this(0, null);
}
// post: constructs a node with given data and null link
public ListNode(int data) {
this(data, null);
}
// post: constructs a node with given data and given link
public ListNode(int data, ListNode next) {
ALL_NODES.add(this);
this.data = data;
this.next = next;
this.visited = false;
this.cycle = false;
}
public ListNode __gotoNext() {
return __gotoNext(true);
}
public ListNode __gotoNext(boolean checkForCycle) {
if (checkForCycle) {
visited = true;
if (next != null) {
if (next.visited) {
// throw new IllegalStateException("cycle detected in list");
next.cycle = true;
}
next.visited = true;
}
}
return next;
}
}
// YOUR CODE GOES HERE
}
解决方法:
这是带有打印语句的代码：
public void reverse() {
System.out.println(toFormattedString());
int x = this.size();
this.add(front.data);
System.out.println(toFormattedString());
for (int i = 0; i < x; i++) {
this.remove(0);
System.out.println(toFormattedString());
this.add(this.size() - 1, front.data);
System.out.println(toFormattedString());
}
}
输出：
front -> [1] -> [2] -> [3] -> [4] -> [5] /
front -> [1] -> [2] -> [3] -> [4] -> [5] -> [1] /
front -> [2] -> [3] -> [4] -> [5] -> [1] /
front -> [2] -> [3] -> [4] -> [5] -> [2] -> [1] /
front -> [3] -> [4] -> [5] -> [2] -> [1] /
front -> [3] -> [4] -> [5] -> [2] -> [3] -> [1] /
front -> [4] -> [5] -> [2] -> [3] -> [1] /
front -> [4] -> [5] -> [2] -> [3] -> [4] -> [1] /
front -> [5] -> [2] -> [3] -> [4] -> [1] /
front -> [5] -> [2] -> [3] -> [4] -> [5] -> [1] /
front -> [2] -> [3] -> [4] -> [5] -> [1] /
front -> [2] -> [3] -> [4] -> [5] -> [2] -> [1] /
希望这可以帮助.
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