1、用两个栈实现队列、

import java.util.Stack;public class Solution {Stack<Integer>stack1=new Stack<Integer>();Stack<Integer>stack2=new Stack<Integer>();public void push(int node){stack1.push(node);}public int pop(){while(!stack1.isEmpty()){stack2.push(stack1.pop());}int res= stack2.pop();while(!stack2.isEmpty()){stack1.push(stack2.pop());}return res;}//以上为牛客输入、public static void main(String[] args) {Solution solution = new Solution();// 示例1String[] operations1 = {"PSH1", "PSH2", "POP", "POP"};int[] expected1 = {1, 2};int[] result1 = performOperations(solution, operations1);System.out.println("Expected: " + arrayToString(expected1) + ", Actual: " + arrayToString(result1));// 示例2String[] operations2 = {"PSH2", "POP", "PSH1", "POP"};int[] expected2 = {2, 1};int[] result2 = performOperations(solution, operations2);System.out.println("Expected: " + arrayToString(expected2) + ", Actual: " + arrayToString(result2));}private static int[] performOperations(Solution solution, String[] operations) {int popCount = 0;for (String operation : operations) {if (operation.startsWith("PSH")) {int value = Integer.parseInt(operation.substring(3));solution.push(value);} else if (operation.equals("POP")) {popCount++;}}int[] result = new int[popCount];for (int i = 0; i < popCount; i++) {result[i] = solution.pop();}return result;}private static String arrayToString(int[] array) {StringBuilder sb = new StringBuilder();for (int num : array) {sb.append(num).append(" ");}return sb.toString().trim();//去除前后导、}
}

2、包含min函数的栈、

import java.util.Stack;public class min_stack {Stack<Integer>s1=new Stack<Integer>();//用于栈的push和pop、Stack<Integer>s2=new Stack<Integer>();//用于存储最小min、public void push(int node){s1.push(node);if(s2.isEmpty()||s2.peek()>node){s2.push(node);}else{s2.push(s2.peek());}}public void pop(){s1.pop();s2.pop();}public int top(){return s1.peek();}public int min(){return s2.peek();}public static void main(String[] args) {String[] input = {"PSH-1", "PSH2", "MIN", "TOP", "POP", "PSH1", "TOP", "MIN"};min_stack stack = new min_stack();for (String command : input) {if (command.startsWith("PSH")) {int value = Integer.parseInt(command.substring(3));stack.push(value);} else if (command.equals("POP")) {stack.pop();} else if (command.equals("TOP")) {System.out.print(stack.top() + ",");} else if (command.equals("MIN")) {System.out.print(stack.min() + ",");}}}
}