数据结构-两个栈实现一个队列和两个队列实现一个栈

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两个栈实现一个队列

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import java.util.Stack;
/**
 * Created by cdx0312
 * 2018/4/13
 */
public class TwoStackImpQueue {
    private Stack<Integer> stack1 = new Stack<>();
    private Stack<Integer> stack2 = new Stack<>();
    public void push(int node) {
        stack1.push(node);
    }
    public Integer pop() {
        if (stack2.size() <= 0) {
            while (stack1.size() > 0) {
                stack2.push(stack1.pop());
            }
        }
        if (stack2.isEmpty()) {
            try {
                throw new Exception("queue is empty");
            } catch (Exception e){
                e.printStackTrace();
            }
        }
        return stack2.pop();
    }
}

两个队列实现一个栈

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import java.util.LinkedList;
import java.util.Queue;
/**
 * Created by cdx0312
 * 2018/4/13
 */
public class TwoListImpStack {
    private Queue<Integer> list1 = new LinkedList<>();
    private Queue<Integer> list2 = new LinkedList<>();
    public void push(int node) {
        if (list1.isEmpty() && list2.isEmpty()){
            list1.add(node);
        } else if (list1.isEmpty()) {
            list2.add(node);
        } else {
            list2.add(node);
        }
    }
    public Integer pop() {
        if (list1.isEmpty() && list2.isEmpty()){
            try {
                throw new Exception("stack is Empty!");
            } catch (Exception e) {
                e.printStackTrace();
            }
        } else if (list1.isEmpty()) {
            while (list2.size() > 1) {
                list1.add(list2.poll());
            }
            return list2.poll();
        } else {
            while (list1.size() > 1) {
                list2.add(list1.poll());
            }
            return list1.poll();
        }
        return null;
    }
}
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