[알고리즘] 백준 10828번 스택 (JAVA)

1. 배열로 스택 구현하여 문제풀이

import java.util.Scanner;

class Stack{
	private int[] stack;
	private int topIndex = -1;
	
	Stack(){
		
	}
	
	Stack(int number){ // 배열의 크기는 최대 명령어 수이다.
		stack = new int[number];
	}
	
	public void push(int x) {
		stack[++topIndex] = x;
	}
	
	public int pop() {
		if (isEmpty()) {
			return -1;
		}
		else {
			return stack[topIndex--];
		}
	}
	
	public int size() {
		return topIndex + 1;
	}
	
	public boolean isEmpty() {
		if(size()==0)
			return true;
		else
			return false;
	}
	
	public int top() {
		if(isEmpty())
			return -1;
		else
			return stack[topIndex];
	}
}

public class Main {
	public static void main(String args[]) {
		Scanner scanner = new Scanner(System.in);
		int number = scanner.nextInt();
		Stack stack = new Stack(number);
		for(int i = 0; i <number; i++) {
			String command = scanner.next();
			switch(command) {
				case "push":
					int x = scanner.nextInt();
					stack.push(x);
					break;
				case "pop":
					System.out.println(stack.pop());
					break;
				case "empty":
                	if(stack.isEmpty())
						System.out.println(1);
                    else
                    	System.out.println(0);
					break;
				case "top":
					System.out.println(stack.top());
					break;
				case "size":
					System.out.println(stack.size());
					break;
			}
		}
	}
}

 

2. Stack 라이브러리를 이용하여 문제풀이

import java.util.Scanner;
import java.util.Stack;

public class Main {
	public static void main(String args[]) {
		Scanner scanner = new Scanner(System.in);
		int number = scanner.nextInt();
		Stack stack = new Stack();
		for(int i = 0; i <number; i++) {
			String command = scanner.next();
			switch(command) {
				case "push":
					int x = scanner.nextInt();
					stack.push(x);
					break;
				case "pop":
					if (stack.isEmpty())
						System.out.println(-1);
					else
						System.out.println(stack.pop());
					break;
				case "empty":
					if (stack.isEmpty())
						System.out.println(1);
					else
						System.out.println(0);
					break;
				case "top":
					if (stack.isEmpty())
						System.out.println(-1);
					else
						System.out.println(stack.peek());
					break;
				case "size":
					System.out.println(stack.size());
					break;
			}
		}
	}
}