【一起学算法】 - 栈 & 队列

文章前言

• 【一起学算法】专栏持续更新中，会在这里记录算法学习的过程
• 文末获取【一起学算法】Github仓库手写算法源码，一起跟着写一遍吧~
• 【一起学算法】中所涉及的部分关于leetcode中的原题均可在leetcode官网的运行器通关~

栈

栈的概念就是: 数据先进后出（子弹匣原理）

手写栈

主要功能

单链表实现

思路图解

关键代码

/**
 * @author Rhys.Ni
 * @version 1.0
 * @date 2021/12/9 2:45 上午
 * @Description
 */
public class MyStack<T> {
    private Node<T> head;
    private int size;

    public int size() {
        return this.size;
    }

    public Boolean isEmpty() {
        return size == 0;
    }

    /**
     * 压栈
     * @param value
     */
    public void push(T value) {
        //遵循队列先进后出
        //从头节点开始弹出，符合队列先进后出机制
        Node<T> currNode = new Node<>(value);
        if (head != null) {
            currNode.next = head;
        }
        head = currNode;
        size++;
    }

    /**
     * 弹栈
     * @return
     */
    public T pop() {
        T val = null;
        if (head != null) {
            val = head.value;
            head = head.next;
            size--;
        }
        return val;
    }

    /**
     * 查看栈顶值
     * @return
     */
    public T peek() {
        return head == null ? null : head.value;
    }
}

队列

数据先进先出（排队）

手写队列

主要功能

单链表实现

思路图解

关键代码

/**
 * @author Rhys.Ni
 * @version 1.0
 * @date 2021/12/9 12:05 上午
 * @Description
 */
public class MyQueue<T> {
    private Node<T> head;
    private Node<T> tail;
    private int size;


    public int size() {
        return this.size;
    }

    public Boolean isEmpty() {
        return size == 0;
    }

    public void offer(T value) {
        //遵循队列先进先出
        //从头节点开始弹出，符合队列先进先出机制
        Node<T> currNode = new Node<>(value);
        if (tail == null) {
            head = currNode;
            tail = currNode;
        } else {
            tail.next = currNode;
            tail = currNode;
        }
        size++;
    }

    public T poll() {
        T value = null;
        if (head != null) {
            //获取当前头结点的值
            value = head.value;
            //让当前头节点的下一个节点成为新的头节点
            head = head.next;
            //每弹出一个值size同步递减
            size--;
        }
        if (head==null){
            //说明没有值了，保持头尾节点一致;
            tail = null;
        }
        return value;
    }

    public T peek() {
        T value = null;
        if (head != null) {
            //获取当前头结点的值
            value = head.value;
        }
        return value;
    }

    public MyQueue() {
        this.head = null;
        this.tail = null;
        this.size = 0;
    }
}

手写双端队列

主要功能

思路图解

关键代码

/**
 * @author Rhys.Ni
 * @version 1.0
 * @date 2021/12/13 1:34 上午
 * @Description
 */
public class MyDeque<T> {
    private DoubleNode<T> head;
    private DoubleNode<T> tail;
    private int size;

    public void pushHead(T value) {
        DoubleNode<T> curr = new DoubleNode<>(value);
        if (head == null) {
            head = curr;
            tail = curr;
        } else {
            head.last = curr;
            curr.next = head;
            head = curr;
        }
        size++;
    }

    public void pushTail(T value) {
        DoubleNode<T> curr = new DoubleNode<>(value);
        if (head == null) {
            head = curr;
            tail = curr;
        } else {
            tail.next = curr;
            curr.last = tail;
            tail = curr;
        }
        size++;
    }

    public T pollHead() {
        T value = null;
        if (head == null) {
            return value;
        }
        value = head.value;
        if (head == tail) {
            head = null;
            tail = null;
        } else {
            head = head.next;
            head.last = null;
        }
        size--;
        return value;
    }

    public T pollTail() {
        T value = null;
        if (tail == null) {
            return value;
        }
        value = tail.value;
        if (tail == head) {
            tail = null;
            head = null;
        } else {
            tail = tail.last;
            tail.next = null;
        }
        size--;
        return value;
    }

    public T peekHead() {
        T value = null;
        if (!isEmpty()) {
            value = head.value;
        }
        return value;
    }

    public T peekTail() {
        T value = null;
        if (!isEmpty()) {
            value = tail.value;
        }
        return value;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public int size() {
        return size;
    }

    public MyDeque() {
        this.head = null;
        this.tail = null;
        this.size = 0;
    }
}

源码获取地址

加油小伙伴~ 点击获取算法篇代码~