单链表实现队列和栈
作者：互联网
package class04;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;
/**
* 单链表实现队列和栈
*/
public class Code02_LinkedListToQueueAndStack {
public static class Node<V> {
public V value;
public Node<V> next;
public Node(V v) {
value = v;
next = null;
}
}
//实现队列
public static class MyQueue<V> {
private Node<V> head;
private Node<V> tail;
private int size;
public MyQueue() {
head = null;
tail = null;
size = 0;
}
public boolean isEmpty() {
return size == 0;
}
public int size() {
return size;
}
//队列添加元素的方法
public void offer(V value) {
Node<V> cur = new Node<>(value);
// if (head == null) {
if (tail == null) {
head = cur;
tail = cur;
} else {
tail.next = cur;
tail = cur;
}
size++;
}
//队列弹出元素的方法
public V poll() {
V ans = null;
if (head != null) {
System.out.println("node1");
ans = head.value;
head = head.next;
size--;
}
//为什么方式1会报空指针异常？方式2就不会报空指针异常？
//因为上方的if执行完后，head有可能变成了null，所以head == null的情况，要单独判断。而不是使用else。
// else {//head == null//方式1
// System.out.println("node2");
// tail = null;
// }
// printMyQueue(head);
if (head == null) {//方式2
System.out.println("node2");
tail = null;
}
return ans;
}
//队列返回将要弹出，但是实际并不弹出的元素
public V peek() {
V ans = null;
if (head != null) {
ans = head.value;
}
return ans;
}
}
//实现栈
public static class MyStack<V> {
private Node<V> head;
private int size;
public MyStack() {
head = null;
size = 0;
}
public boolean isEmpty() {
return size == 0;
}
public int size() {
return size;
}
//栈添加元素
public void push(V value) {
Node<V> cur = new Node<>(value);
if (head == null) {
head = cur;
} else {
cur.next = head;
head = cur;
}
size++;
}
//栈弹出元素
public V pop() {
V ans = null;
if (head != null) {
ans = head.value;
head = head.next;
size--;
}
return ans;
}
//栈将要弹出，但是实际并不弹出的元素
public V peek() {
return head == null ? null : head.value;
}
}
//测试队列
public static void testQueue() {
try {
MyQueue<Integer> myQueue = new MyQueue<>();
Queue<Integer> test = new LinkedList<>();
int testTimes = 1000;
int maxValue = 1280;
System.out.println("test begin!");
for (int i = 0; i < testTimes; i++) {
if (myQueue.isEmpty() != test.isEmpty()) {
System.out.println("Oops1!");
}
if (myQueue.size != test.size()) {
System.out.println("Oops2!");
}
double decide = Math.random();
if (decide < 0.33) {
int num = (int) (Math.random() * maxValue);
myQueue.offer(num);
test.offer(num);
} else if (decide < 0.66) {
if (!myQueue.isEmpty()) {
Integer num = myQueue.poll();
Integer num2 = test.poll();
System.out.println("num2 = " + num2);
System.out.println("num = " + num);
//如果不使用equals()，而是使用!=。那么当num大于等于128时，结果就会是false。所以改为使用equals()。
//if (num != num2) {
if (!num.equals(num2)) {
System.out.println("Oops3!");
}
}
} else {
if (!myQueue.isEmpty()) {
// int num = myQueue.peek();
// int num2 = test.peek();
Integer num = myQueue.peek();
Integer num2 = test.peek();
if (!num.equals(num2)) {
System.out.println("Oops4!");
}
}
}
}
if (myQueue.size() != test.size()) {
System.out.println("Oops5!");
}
while (!myQueue.isEmpty()) {
Integer num = myQueue.poll();
Integer num2 = test.poll();
if (!num.equals(num2)) {
System.out.println("Oops6!");
}
}
System.out.println("test finished!");
} catch (Exception e) {
e.printStackTrace();
}
}
//测试队列
public static void testStack() {
MyStack<Integer> myStack = new MyStack<>();
Stack<Integer> testStack = new Stack<>();
int testTimes = 1000;
int maxValue = 1000;
System.out.println("test MyStack begin!");
for (int i = 0; i < testTimes; i++) {
if (myStack.isEmpty() != testStack.isEmpty()) {
System.out.println("MyStack_Oops1");
}
int size = myStack.size();
int size1 = testStack.size();
if (size != size1) {
System.out.println("MyStack_Oops2!");
}
double random = Math.random();
if (random < 0.33) {
System.out.println("node1");
int num = (int) (Math.random() * maxValue);
myStack.push(num);
testStack.push(num);
} else if (random < 0.66) {
System.out.println("node2");
if (!myStack.isEmpty()) {
// if (!myStack.pop().equals(testStack.pop())) {
Integer pop = myStack.pop();
Integer pop1 = testStack.pop();
System.out.println("pop = " + pop);
System.out.println("pop1 = " + pop1);
if (!pop1.equals(pop)) {
System.out.println("MyStack_Oops3!");
}
}
} else {
System.out.println("node3");
if (!myStack.isEmpty()) {
Integer peek = testStack.peek();
Integer peek1 = myStack.peek();
System.out.println("peek = " + peek);
System.out.println("peek1 = " + peek1);
if (!peek.equals(peek1)) {
System.out.println("MyStack_Oops4!");
}
}
}
}
System.out.println("test MyStack finish!");
}
private static void printMyQueue(Node head) {
while (head != null) {
System.out.print(head.value + " ");
head = head.next;
}
System.out.println();
}
public static void main(String[] args) {
testQueue();
testStack();
}
}
标签：head,单链,队列,System,实现,println,size,public,out 来源： https://www.cnblogs.com/TheFloorIsNotTooHot/p/16535998.html