Java模拟栈和队列数据结构的基本示例讲解

栈和队列：
一般是作为程序员的工具，用于辅助构思算法，生命周期较短，运行时才被创建；
访问受限，在特定时刻，只有一个数据可被读取或删除；
是一种抽象的结构，内部的实现机制，对用户不可见，比如用数组、链表来实现栈。

模拟栈结构
同时，只允许一个数据被访问，后进先出
对于入栈和出栈的时间复杂度都为o(1),即不依赖栈内数据项的个数，操作比较快
例，使用数组作为栈的存储结构

public class stacks<t> { 
  private int max; 
  private t[] ary; 
  private int top;  //指针，指向栈顶元素的下标 
   
  public stacks(int size) { 
    this.max = size; 
    ary = (t[]) new object[max]; 
    top = -1; 
  } 
   
  // 入栈 
  public void push(t data) { 
    if (!isfull()) 
      ary[++top] = data; 
  } 
   
  // 出栈 
  public t pop() { 
    if (isempty()) { 
      return null; 
    } 
    return ary[top--]; 
  } 
   
  // 查看栈顶 
  public t peek() { 
    return ary[top]; 
  } 
   
  //栈是否为空 
  public boolean isempty() { 
    return top == -1; 
  } 
   
  //栈是否满 
  public boolean isfull() { 
    return top == max - 1; 
  } 
   
  //size 
  public int size() { 
    return top + 1; 
  } 
   
  public static void main(string[] args) { 
    stacks<integer> stack = new stacks<integer>(3); 
    for (int i = 0; i < 5; i++) { 
      stack.push(i); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 0; i < 5; i++) { 
      integer peek = stack.peek(); 
      system.out.println("peek:" + peek); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 0; i < 5; i++) { 
      integer pop = stack.pop(); 
      system.out.println("pop:" + pop); 
      system.out.println("size:" + stack.size()); 
    } 
     
    system.out.println("----"); 
     
    for (int i = 5; i > 0; i--) { 
      stack.push(i); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 5; i > 0; i--) { 
      integer peek = stack.peek(); 
      system.out.println("peek:" + peek); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 5; i > 0; i--) { 
      integer pop = stack.pop(); 
      system.out.println("pop:" + pop); 
      system.out.println("size:" + stack.size()); 
    } 
  } 
} 

上面的例子，有一个maxsize的规定，因为数组是要规定大小的，若想无限制，可以使用其他结构来做存储，当然也可以new一个新的长度的数组。
例，使用linkedlist存储来实现栈

public class stackss<t> { 
  private linkedlist<t> datas; 
   
  public stackss() { 
    datas = new linkedlist<t>(); 
  } 
   
  // 入栈 
  public void push(t data) { 
    datas.addlast(data); 
  } 
   
  // 出栈 
  public t pop() { 
    return datas.removelast(); 
  } 
   
  // 查看栈顶 
  public t peek() { 
    return datas.getlast(); 
  } 
   
  //栈是否为空 
  public boolean isempty() { 
    return datas.isempty(); 
  } 
   
  //size 
  public int size() { 
    return datas.size(); 
  } 
   
  public static void main(string[] args) { 
    stacks<integer> stack = new stacks<integer>(3); 
    for (int i = 0; i < 5; i++) { 
      stack.push(i); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 0; i < 5; i++) { 
      integer peek = stack.peek(); 
      system.out.println("peek:" + peek); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 0; i < 5; i++) { 
      integer pop = stack.pop(); 
      system.out.println("pop:" + pop); 
      system.out.println("size:" + stack.size()); 
    } 
     
    system.out.println("----"); 
    for (int i = 5; i > 0; i--) { 
      stack.push(i); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 5; i > 0; i--) { 
      integer peek = stack.peek(); 
      system.out.println("peek:" + peek); 
      system.out.println("size:" + stack.size()); 
    } 
    for (int i = 5; i > 0; i--) { 
      integer pop = stack.pop(); 
      system.out.println("pop:" + pop); 
      system.out.println("size:" + stack.size()); 
    } 
  } 
} 

例，单词逆序，使用statck结构

public class wordreverse { 
   
  public static void main(string[] args) { 
    reverse("株式会社"); 
  } 
   
  static void reverse(string word) { 
    if (word == null) return; 
    stackss<character> stack = new stackss<character>(); 
    char[] chararray = word.tochararray(); 
    int len = chararray.length; 
    for (int i = 0; i <len; i++ ) { 
      stack.push(chararray[i]); 
    } 
    stringbuilder sb = new stringbuilder(); 
    while (!stack.isempty()) { 
      sb.append(stack.pop()); 
    } 
    system.out.println("反转后：" + sb.tostring()); 
  } 
} 

打印：

反转后：社会式株 

模拟队列(一般队列、双端队列、优先级队列)
队列：
先进先出，处理类似排队的问题，先排的，先处理，后排的等前面的处理完了，再处理
对于插入和移除操作的时间复杂度都为o(1)，从后面插入，从前面移除
双端队列：
即在队列两端都可以insert和remove：insertleft、insertright，removeleft、removeright
含有栈和队列的功能，如去掉insertleft、removeleft，那就跟栈一样了；如去掉insertleft、removeright，那就跟队列一样了
一般使用频率较低，时间复杂度 o(1)
优先级队列：
内部维护一个按优先级排序的序列。插入时需要比较查找插入的位置，时间复杂度o(n)， 删除o(1)
 

/* 
 * 队列  先进先出，一个指针指示插入的位置，一个指针指示取出数据项的位置 
 */ 
public class queueq<t> { 
  private int max; 
  private t[] ary; 
  private int front; //队头指针 指示取出数据项的位置 
  private int rear; //队尾指针 指示插入的位置 
  private int nitems; //实际数据项个数 
   
  public queueq(int size) { 
    this.max = size; 
    ary = (t[]) new object[max]; 
    front = 0; 
    rear = -1; 
    nitems = 0; 
  } 
  //插入队尾 
  public void insert(t t) { 
    if (rear == max - 1) {//已到实际队尾，从头开始 
      rear = -1; 
    } 
    ary[++rear] = t; 
    nitems++; 
  } 
  //移除队头 
  public t remove() { 
    t temp = ary[front++]; 
    if (front == max) {//列队到尾了，从头开始 
      front = 0; 
    } 
    nitems--; 
    return temp; 
  } 
  //查看队头 
  public t peek() { 
    return ary[front]; 
  } 
   
  public boolean isempty() { 
    return nitems == 0; 
  } 
   
  public boolean isfull() { 
    return nitems == max; 
  } 
   
  public int size() { 
    return nitems; 
  } 
   
  public static void main(string[] args) { 
    queueq<integer> queue = new queueq<integer>(3); 
    for (int i = 0; i < 5; i++) { 
      queue.insert(i); 
      system.out.println("size:" + queue.size()); 
    } 
    for (int i = 0; i < 5; i++) { 
      integer peek = queue.peek(); 
      system.out.println("peek:" + peek); 
      system.out.println("size:" + queue.size()); 
    } 
    for (int i = 0; i < 5; i++) { 
      integer remove = queue.remove(); 
      system.out.println("remove:" + remove); 
      system.out.println("size:" + queue.size()); 
    } 
     
    system.out.println("----"); 
     
    for (int i = 5; i > 0; i--) { 
      queue.insert(i); 
      system.out.println("size:" + queue.size()); 
    } 
    for (int i = 5; i > 0; i--) { 
      integer peek = queue.peek(); 
      system.out.println("peek:" + peek); 
      system.out.println("size:" + queue.size()); 
    } 
    for (int i = 5; i > 0; i--) { 
      integer remove = queue.remove(); 
      system.out.println("remove:" + remove); 
      system.out.println("size:" + queue.size()); 
    } 
  } 
   
} 

/* 
 * 双端队列<span style="white-space:pre"> </span>两端插入、删除 
 */ 
public class queueqt<t> { 
  private linkedlist<t> list; 
 
  public queueqt() { 
    list = new linkedlist<t>(); 
  } 
 
  // 插入队头 
  public void insertleft(t t) { 
    list.addfirst(t); 
  } 
 
  // 插入队尾 
  public void insertright(t t) { 
    list.addlast(t); 
  } 
 
  // 移除队头 
  public t removeleft() { 
    return list.removefirst(); 
  } 
 
  // 移除队尾 
  public t removeright() { 
    return list.removelast(); 
  } 
 
  // 查看队头 
  public t peekleft() { 
    return list.getfirst(); 
  } 
 
  // 查看队尾 
  public t peekright() { 
    return list.getlast(); 
  } 
 
  public boolean isempty() { 
    return list.isempty(); 
  } 
 
  public int size() { 
    return list.size(); 
  } 
 
} 

/* 
 * 优先级队列  队列中按优先级排序，是一个有序的队列 
 */ 
public class queueqp { 
  private int max; 
  private int[] ary; 
  private int nitems; //实际数据项个数 
   
  public queueqp(int size) { 
    this.max = size; 
    ary = new int[max]; 
    nitems = 0; 
  } 
  //插入队尾 
  public void insert(int t) { 
    int j; 
    if (nitems == 0) { 
      ary[nitems++] = t; 
    } else { 
      for (j = nitems - 1; j >= 0; j--) { 
        if (t > ary[j]) { 
          ary[j + 1] = ary[j]; //前一个赋给后一个 小的在后    相当于用了插入排序，给定序列本来就是有序的，所以效率o(n) 
        } else { 
          break; 
        } 
      } 
      ary[j + 1] = t; 
      nitems++; 
    } 
    system.out.println(arrays.tostring(ary)); 
  } 
  //移除队头 
  public int remove() { 
    return ary[--nitems]; //移除优先级小的 
  } 
  //查看队尾 优先级最低的 
  public int peekmin() { 
    return ary[nitems - 1]; 
  } 
   
  public boolean isempty() { 
    return nitems == 0; 
  } 
   
  public boolean isfull() { 
    return nitems == max; 
  } 
   
  public int size() { 
    return nitems; 
  } 
   
  public static void main(string[] args) { 
    queueqp queue = new queueqp(3); 
    queue.insert(1); 
    queue.insert(2); 
    queue.insert(3); 
    int remove = queue.remove(); 
    system.out.println("remove:" + remove); 
     
  } 
   
}