"Niuke | daily question" template stack

Author's brief introduction ： One likes to write , Sophomore rookie of planning major

Personal home page ：starry Lu Li

First date ：2022 year 7 month 13 Wednesday, Sunday

Last article ：『 First issue article 』

Subscription column ：『 Collection of Niuke brush questions 』

Daily recommendation ： Basic algorithm is a very important part in both graduate interview and job interview , Here we recommend an algorithm interview artifact ： Cattle from - Interview artifact ; Algorithm problems can only be kept thinking and feeling by brushing more and more frequently , Let's move quickly （ reminder ： The common interview question bank is also very nice Oh ）

If the article helps you, remember to praise + Collect and support

1. A daily topic ：AB1 【 Templates 】 Stack

Portal ： A daily topic ：AB1 【 Templates 】 Stack

2. Test examples

Input ：

6
push 1
pop
top
push 2
push 3
pop

Output ：

1
error
3

3.Stack Class implementation

Let's start with a simple use Java Self contained Stack Class to achieve , In this way, we only need to process the input and judge the blank

import java.util.*;
public class Main {
    
    public static void main(String[] args) {
    
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        scanner.nextLine();
        String string;
        Stack<Integer> stack = new Stack<Integer>();
        while (n-- != 0) {
    
            string = scanner.nextLine();
            String cmp = string.substring(0, 3);
            if (cmp.equals("pus")) {
    
                int a = Integer.valueOf(string.substring(5, string.length()));
                stack.push(a);
            } else if (cmp.equals("pop")) {
    
                if (!stack.isEmpty()) {
    
                    System.out.println(stack.pop());
                } else {
    
                    System.out.println("error");
                }
            } else if (cmp.equals("top")) {
    
                if (!stack.isEmpty()) {
    
                    System.out.println(stack.peek());
                } else {
    
                    System.out.println("error");
                }
            }

        }
    }
}

4. Array implementation stack

It's not challenging to write with your own class ？？？ Then write one by yourself MyStack Class implements stack with array

import java.util.*;
public class Main{
    
    public static void main(String[] args){
    
        Scanner scanner=new Scanner(System.in);
        int n=scanner.nextInt();
        scanner.nextLine();
        String string;
        MyStack stack=new MyStack(n+1);
        while(n--!=0){
    
            string=scanner.nextLine();
            String cmp=string.substring(0,3);
            if(cmp.equals("pus")){
    
                int a=Integer.valueOf(string.substring(5,6));
                stack.push(a);
            }else if(cmp.equals("pop")){
    
                stack.pop();
            }else if(cmp.equals("top")){
    
                stack.peek();
            }
        }
        scanner.close();
    }
}

class MyStack{
    
	int[] data;// Stack with arrays 
	int maxSize;// Stack capacity 
	int top=-1;// Top pointer of stack - The number of elements in the stack 
	
	// Constructors 
	public MyStack(int maxSize) {
    
		this.maxSize=maxSize;// Specify stack size in advance 
		this.data=new int[maxSize];// Initialize stack space 
	}
	// Push 
	public void push(int val) {
    
		if(this.top==this.maxSize) {
    // Stack full - The number of elements in the stack is equal to the capacity of the stack 
			System.out.println("error");
		}else {
    
			// The stack is not full , Move the stack top pointer , Add new elements 
			data[++this.top]=val;
		}
	}
	// The stack, 
	public void pop() {
    
		// The stack is empty - The elements in the stack are 0
		if(this.isEmpty()) {
    
			System.out.println("error");
		}else {
    
			// The stack is not empty , Print top of stack elements , The top of the stack pointer moves down 
			System.out.println(data[this.top--]);
		}
	}
	// Print top of stack elements 
	public void peek() {
    
		// The stack is empty - The elements in the stack are 0
		if(this.isEmpty()) {
    
			System.out.println("error");
		}else {
    
			// The stack is not empty , Print top of stack elements 
			System.out.println(data[this.top]);
		}
	}
	
	// Empty stack 
	public boolean isEmpty() {
    
		if(this.top==-1) {
    
			return true;
		}else {
    
			return false;
		}
	}
}

Daily recommendation ： Basic algorithm is a very important part in both graduate interview and job interview , Here we recommend an algorithm interview artifact ： Cattle from - Interview artifact ; Algorithm problems can only be kept thinking and feeling by brushing more and more frequently , Let's move quickly （ reminder ： The common interview question bank is also very nice Oh ）

If the article helps you, remember to praise + Collect and support