解题思路:
注意事项:
参考代码:
import java.util.ArrayList; import java.util.Scanner; public class T1733 { public static void main(String[] args) { Scanner in = new Scanner(System.in); while(in.hasNext()){ int n = in.nextInt(); if(n == 0) break; in.nextLine(); ArrayList<Integer> l = new ArrayList<Integer>(); for(int i = 0;i<n;i++){ String s = in.nextLine(); if(s.charAt(0) == 'P'){ int data = Integer.parseInt(s.substring(2,s.length())); l.add(data); } else if(s.charAt(0) == 'O' && !l.isEmpty()){ l.remove(l.size()-1); } else if(s.charAt(0) == 'A'){ if(!l.isEmpty()) System.out.println(l.get(l.size()-1)); else System.out.println("E"); } } System.out.println(); } in.close(); } }
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