백준 1874번: 스택 수열

문제 출처: https://www.acmicpc.net/problem/1874

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Stack;
 
public class algo6_1874_stack_sequence {
 
    public static void main(String[] args) throws NumberFormatException, IOException {
        BufferedReader reader= new BufferedReader(new InputStreamReader(System.in));
        StringBuilder builder = new StringBuilder();
        
        int N = Integer.parseInt(reader.readLine());
        Stack<Integer> stack = new Stack<>();
        boolean isPossible = true;
    
        for(int i=0, j=1 ; i<N ; i++){
            int input = Integer.parseInt(reader.readLine());
            if(!isPossible)
                continue;
            
            while(j <= input){
                stack.push(j++);
                builder.append("+\n");
            }
            if(stack.peek() == input){
                stack.pop();
                builder.append("-\n");
            }
            else{
                builder = new StringBuilder("NO\n");
                isPossible = false;
            }
        }
        
        System.out.println(builder);
    }
}