用雙向鏈表實現棧和隊列

1.棧和隊列概念

棧和隊列是一種邏輯上的數據結構：

• "棧”（Stack）的本意是乾草堆;描述一種數據後入先出 LIFO (LastInput First Out)
• “隊列”（Queue）就是等待做某事而排成的隊;描述一種先入先出 FIFO（First Input First Out）
  參考：《計算機是怎麼跑起來的》-[日]矢澤久雄 第6.4章節

2.實現方式

• 用雙向鏈表

import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;

/**
 * 雙向鏈表實現棧和隊列
 *
 * @author TaoistQu
 */
public class DoubleEndsQueueToStackAndQueue {
    /**
     * 實現一個雙向鏈表結構，可以從頭部和尾部依次添加元素
     * 也可以從頭部和尾部刪除元素
     *
     * @param <T>
     */
    public static class DoubleEndsQueue<T> {
        public Node<T> head;
        public Node<T> tail;

        /**
         * 從頭部加節點
         *
         * @param value
         */
        public void addFromHead(T value) {
            Node<T> cur = new Node<>(value);
            if (head == null) {
                head = cur;
                tail = cur;
            } else {
                cur.next = head;
                head.last = cur;
                head = cur;
            }
        }

        /**
         * 從尾部加節點
         *
         * @param value
         */
        public void addFromBottom(T value) {
            Node<T> cur = new Node<>(value);
            if (head == null) {
                head = cur;
                tail = cur;
            } else {
                cur.last = tail;
                tail.next = cur;
                tail = cur;
            }
        }

        /**
         * 從頭部彈出元素
         *
         * @return
         */
        public T popFromHead() {
            if (head == null) {
                return null;
            }
            Node<T> cur = head;
            if (head == tail) {
                head = null;
                tail = null;
            } else {
                head = head.next;
                head.last = null;
                cur.next = null;
            }
            return cur.value;
        }

        public T popFromBottom() {
            if (head == null) {
                return null;
            }
            Node<T> cur = tail;
            if (tail == head) {
                head = null;
                tail = null;
            } else {
                tail = tail.last;
                tail.next = null;
                cur.last = null;
            }
            return cur.value;
        }

        public boolean isEmpty() {
            return head == null;
        }
    }

    /**
     * 用雙向鏈表實現棧
     *
     * @param <T>
     */
    public static class MyStack<T> {
        private DoubleEndsQueue<T> queue;

        public MyStack() {
            queue = new DoubleEndsQueue<>();
        }

        public void push(T value) {
            queue.addFromHead(value);
        }

        public T pop() {
            return queue.popFromHead();
        }

        public boolean isEmpty() {
            return queue.isEmpty();
        }
    }

    /**
     * 用雙向鏈表實現隊列
     *
     * @param <T>
     */
    public static class MyQueue<T> {
        private DoubleEndsQueue<T> queue;

        public MyQueue() {
            queue = new DoubleEndsQueue<>();
        }

        public void push(T value) {
            queue.addFromHead(value);
        }

        public T poll() {
            return queue.popFromBottom();
        }

        public boolean isEmpty() {
            return queue.isEmpty();
        }
    }

    public static boolean isEqual(Integer o1, Integer o2) {
        if (o1 == null && o2 != null) {
            return false;
        }
        if (o1 != null && o2 == null) {
            return false;
        }
        if (o1 == null && o2 == null) {
            return true;
        }
        return o1.equals(o2);
    }

    public static void main(String[] args) {
        int oneTestDataNum = 100;
        int value = 10000;
        int testTimes = 100000;
        for (int i = 0; i < testTimes; i++) {
            MyStack<Integer> myStack = new MyStack<>();
            MyQueue<Integer> myQueue = new MyQueue<>();
            Stack<Integer> stack = new Stack<>();
            Queue<Integer> queue = new LinkedList<>();

            for (int j = 0; j < oneTestDataNum; j++) {
                int nums = (int) (Math.random() * value);
                if (stack.isEmpty()) {
                    myStack.push(nums);
                    stack.push(nums);
                } else {
                    if (Math.random() < 0.5) {
                        myStack.push(nums);
                        stack.push(nums);
                    } else {
                        if (!isEqual(myStack.pop(), stack.pop())) {
                            System.out.println("oops!");
                        }
                    }
                }
                int numq = (int) (Math.random() * value);
                if (stack.isEmpty()) {
                    myQueue.push(numq);
                    queue.offer(numq);
                } else {
                    if (Math.random() < 0.5) {
                        myQueue.push(numq);
                        queue.offer(numq);
                    } else {
                        if (!isEqual(myQueue.poll(), queue.poll())) {
                            System.out.println("oops!");
                        }
                    }
                }
            }

        }

        System.out.println("finish!");
    }

    /**
     * 雙向鏈表節點類
     *
     * @param <T>
     */
    public static class Node<T> {
        public T value;
        public Node<T> last;
        public Node<T> next;

        public Node(T data) {
            value = data;
        }
    }
}
用對數器與JDK的棧和隊列進行 100000次隨機測試結果：


finish!

Process finished with exit code 0

github代碼地址

• 用數組方式