相关概念
栈
先进后出，主要 API：push(), pop(), Java 中的主要实现类 Stack()
队列
先进先出，主要 API：offer(), poll(), peek()，Java 中的主要实现类 Queue 接口，如 LinkedList
作业题
232. 用栈实现队列
package jjn.carl.stack_queue; import java.util.Stack; /** * @author Jjn * @since 2023/7/7 22:50 */ public class MyQueue { private final Stack<Integer> first; private final Stack<Integer> second; public MyQueue() { this.first = new Stack<>(); this.second = new Stack<>(); } public void push(int x) { first.push(x); } public int pop() { if (second.isEmpty()) { while (!first.isEmpty()) { second.push(first.pop()); } } return second.pop(); } public int peek() { if (second.isEmpty()) { while (!first.isEmpty()) { second.push(first.pop()); } } return second.peek(); } public boolean empty() { return first.isEmpty() && second.isEmpty(); } public static void main(String[] args) { MyQueue myQueue = new MyQueue(); myQueue.push(1); myQueue.push(2); System.out.println("myQueue.peek() = " + myQueue.peek()); System.out.println("myQueue.pop() = " + myQueue.pop()); System.out.println("myQueue.empty() = " + myQueue.empty()); } }
225. 用队列实现栈
package jjn.carl.stack_queue; import java.util.LinkedList; import java.util.Queue; /** * @author Jjn * @since 2023/7/7 23:03 */ public class MyStack { private final Queue<Integer> first; private final Queue<Integer> second; public MyStack() { this.first = new LinkedList<>(); this.second = new LinkedList<>(); } public void push(int x) { while (!first.isEmpty()) { second.offer(first.poll()); } first.offer(x); while (!second.isEmpty()) { first.offer(second.poll()); } } public int pop() { return first.peek() == null ? -1 : first.poll(); } public int top() { return first.peek() == null ? -1 : first.peek(); } public boolean empty() { return first.isEmpty(); } public static void main(String[] args) { MyStack myStack = new MyStack(); myStack.push(1); myStack.push(2); System.out.println("myStack.top() = " + myStack.top()); System.out.println("myStack.pop() = " + myStack.pop()); System.out.println("myStack.empty() = " + myStack.empty()); } }
