题解 | #【模板】栈#
【模板】栈
https://www.nowcoder.com/practice/104ce248c2f04cfb986b92d0548cccbf
import java.util.ArrayDeque; import java.util.Deque; import java.util.Scanner; public class Main { private static final String PUSH = "push"; private static final String POP = "pop"; private static final String TOP = "top"; public static void main(String[] args) { Scanner in = new Scanner(System.in); final int NUM_OF_OP = in.nextInt(); Deque<Integer> stack = new ArrayDeque<Integer>(); for (int i = 0; i != NUM_OF_OP; ++i) { final String OP = in.next(); if (OP.equals(PUSH)) { stack.push(in.nextInt()); } else if (stack.peek() == null) { System.out.println("error"); } else if (OP.equals(POP)) { System.out.println(stack.pop()); } else { System.out.println(stack.peek()); } } } }