【LeeCode】栈和队列

​​学习参考​​

【栈】

import java.util.*;
// 2022-12-15

// 栈：先进后出
class MyStack {
    public int[] elem;
    public int useSize;

    public MyStack(){
        this.elem = new int[10];
    }

    // 是否栈满
    public boolean isFull(){
        if (this.useSize == this.elem.length){
            return true;
        }
        return false;
    }

    public void push(int item){
        if (isFull()){
            this.elem = Arrays.copyOf(this.elem, 2*2*this.elem.length);
        }
        this.elem[useSize] = item;
        this.useSize++;
    }
    public boolean empty(){
        if (this.useSize == 0) return true;
        return false;
    }

    // 弹出栈顶的值, 删除元素
    public int pop(){
        if (empty()){
            throw new RuntimeException("栈空了");
        }
        int val = this.elem[this.useSize - 1];   // 先进后出   pop输出最后一个
        this.useSize--;
        return val;
    }

    // 弹出栈顶的值， 不删除原来的栈元素
    public int peek(){
        if (empty()){
            throw new RuntimeException("栈空了");
        }
        return this.elem[this.useSize - 1];
    }
}

public class Main{
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6};
        MyStack myStack = new MyStack();
        myStack.elem = arr;
        myStack.useSize = 6;
        myStack.pop();
    }
}

【队列】