QueueWithTwoStacks.java

/**
 * Created by bdl19 on 2017/4/25.
 */
import java.util.Stack;

/**
 * 用两个栈来实现一个队列
 * @author liuxin
 *
 * @param <E>
 */
public class QueueWithTwoStacks<E> {
    private Stack<E> stack1;
    private Stack<E> stack2;


    public QueueWithTwoStacks() {
        stack1 = new Stack<E>();
        stack2 = new Stack<E>();
    }




    public boolean isEmpty() {

        return stack1.isEmpty();
    }



    public int size() {
        return stack1.size();
    }



    public void enQueue(E item) {
        stack1.push(item);
    }

    public E deQueue() {
        E ele ;
        if (stack1.size() == 0) {
            throw new RuntimeException("队列为空！");
        }
        while (stack1.size() > 1) {
            stack2.push(stack1.pop());
        }
        ele =  stack1.pop();
        while(!stack2.isEmpty()){
            stack1.push(stack2.pop());
        }

        return ele;
    }



}