（一）栈和队列--由两个栈组成的队列 java实现

【题目】

编写一个类，用两个栈实现队列，支持队列的基本操作（add、poll、peek）

【代码】

package chapter_1_stackandqueue;

import java.util.Stack;

public class problem02 {
	public static class TwoStackQueqe{
		private Stack stackPush;
		private Stack stackPop;
		
		public TwoStackQueqe() {
			this.stackPush = new Stack();
			this.stackPop = new Stack();
		}
		
		public void add(int pushInt) {
			stackPush.push(pushInt);
		}
		
		public int poll() {
			if (stackPush.empty()&&stackPop.empty()) {
				throw new RuntimeException("Your stack is empty");
			}else if (stackPop.empty()){
				while(!stackPush.empty()) {
					stackPop.push(stackPush.pop());
				}
			}
			return stackPop.pop();
		}
		
		public int peek() {
			if (stackPush.empty()&&stackPop.empty()) {
				throw new RuntimeException("Your stack is empty");
			}else if (stackPop.empty()){
				while(!stackPush.empty()) {
					stackPop.push(stackPush.pop());
				}
			}
			return stackPop.peek();
		}
	}

	public static void main(String[] args) {
		TwoStackQueqe test = new TwoStackQueqe();
		test.add(1);
		test.add(2);
		test.add(3);
		test.add(4);
		test.add(5);
		System.out.println(test.poll());
		System.out.println(test.peek());
		System.out.println(test.poll());
		System.out.println(test.peek());
		System.out.println(test.poll());
		System.out.println(test.peek());
		System.out.println(test.poll());
		System.out.println(test.peek());
		System.out.println(test.poll());
		System.out.println(test.peek());
		System.out.println(test.poll());

	}

}