数据结构栈的java实现

近来复习数据结构，自己动手实现了栈。栈是一种限制插入和删除只能在一个位置上的表。最基本的操作是进栈和出栈，因此，又被叫作“先进后出”表。

实现方式是这样的：首先定义了一个接口，然后通过这个接口实现了线性栈和链式栈，代码比较简单，如下：

package com.peter.java.dsa.interfaces;

/**
 * 栈操作定义
 * 
 * @author Peter Pan
 */

public interface Stack<T> {
    /* 判空 */
    boolean isEmpty();

    /* 清空栈 */
    void clear();

    /* 弹栈 */
    T pop();

    /* 入栈 */
    boolean push(T data);

    /* 栈的长度 */
    int length();

    /* 查看栈顶的元素，但不移除它 */
    T peek();

    /* 返回对象在栈中的位置 */
    int search(T data);
}

线性栈：以数组的方式实现。

package com.peter.java.dsa.common;

import com.peter.java.dsa.interfaces.Stack;

/**
 * 线性栈
 * 
 * @author Peter Pan
 */
public class LinearStack<T> implements Stack<T> {
    @SuppressWarnings("unchecked")
    private T[] t = (T[]) new Object[16];
    private int size = 0;

    @Override
    public boolean isEmpty() {
        // TODO Auto-generated method stub
        return size == 0;
    }

    @Override
    public void clear() {
        // TODO Auto-generated method stub
        for (int i = 0; i < t.length; i++) {
            t[i] = null;
        }
        size = 0;
    }

    @Override
    public T pop() {
        // TODO Auto-generated method stub
        if (size == 0) {
            return null;
        }
        T tmp = t[size - 1];
        t[size - 1] = null;
        size--;
        return tmp;
    }

    @Override
    public boolean push(T data) {
        // TODO Auto-generated method stub
        if (size >= t.length) {
            resize();
        }
        t[size++] = data;
        return true;
    }

    @Override
    public int length() {
        // TODO Auto-generated method stub
        return size;
    }

    @Override
    public T peek() {
        // TODO Auto-generated method stub
        if (size == 0) {
            return null;
        } else {
            return t[size - 1];
        }
    }

    /* return index of data, return -1 if no data */
    @Override
    public int search(T data) {
        // TODO Auto-generated method stub
        int index = -1;
        for (int i = 0; i < t.length; i++) {
            if (t[i].equals(data)) {
                index = i;
                break;
            }
        }
        return index;
    }

    @SuppressWarnings("unchecked")
    private void resize() {
        T[] tmp = (T[]) new Object[t.length * 2];
        for (int i = 0; i < t.length; i++) {
            tmp[i] = t[i];
            t[i] = null;
        }
        t = tmp;
        tmp = null;
    }

    /* from the left to the right is from the top to the bottom of the stack */
    @Override
    public String toString() {
        // TODO Auto-generated method stub
        StringBuffer buffer = new StringBuffer();
        buffer.append("Linear Stack Content:[");
        for (int i = t.length - 1; i > -1; i--) {
            buffer.append(t[i].toString() + ",");
        }
        buffer.append("]");
        buffer.replace(buffer.lastIndexOf(","), buffer.lastIndexOf(",") + 1, "");
        return buffer.toString();
    }

}

链式栈：通过单链表进行实现。

package com.peter.java.dsa.common;

import com.peter.java.dsa.interfaces.Stack;

public class LinkedStack<T> implements Stack<T> {
    private Node top;
    private int size;

    @Override
    public boolean isEmpty() {
        // TODO Auto-generated method stub
        return size == 0;
    }

    @Override
    public void clear() {
        // TODO Auto-generated method stub
        top = null;
        size = 0;
    }

    @Override
    public T pop() {
        // TODO Auto-generated method stub
        T topValue = null;
        if (top != null) {
            topValue = top.data;
            Node oldTop = top;
            top = top.prev;
            oldTop.prev = null;
            size--;
        }
        return topValue;
    }

    @Override
    public boolean push(T data) {
        // TODO Auto-generated method stub
        Node oldTop = top;
        top = new Node(data);
        top.prev = oldTop;
        size++;
        return true;
    }

    @Override
    public int length() {
        // TODO Auto-generated method stub
        return size;
    }

    @Override
    public T peek() {
        // TODO Auto-generated method stub
        T topValue = null;
        if (top != null) {
            topValue = top.data;
        }
        return topValue;
    }

    @Override
    public int search(T data) {
        // TODO Auto-generated method stub
        int index = -1;
        Node tmp = top;
        for (int i = size - 1; i > -1; i--) {
            if (tmp.data.equals(data)) {
                index = i;
                break;
            } else {
                tmp = tmp.prev;
            }
        }
        tmp = null;
        return index;
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        StringBuffer buffer = new StringBuffer();
        buffer.append("Linked Stack Content:[");
        Node tmp = top;
        for (int i = 0; i < size - 1; i++) {
            buffer.append(tmp.toString() + ",");
            tmp = tmp.prev;
        }
        tmp = null;
        buffer.append("]");
        buffer.replace(buffer.lastIndexOf(","), buffer.lastIndexOf(",") + 1, "");
        return super.toString();
    }

    private class Node {
        T data;
        Node prev;

        public Node(T data) {
            // TODO Auto-generated constructor stub
            this.data = data;
        }
    }

}

学习还在进行中，以后会继续更新代码。