LeetCode（剑指 Offer）- 09. 用两个栈实现队列

// 解决方案(1)
class CQueue {
    private final Stack<Integer> stack1 = new Stack<>();
    private final Stack<Integer> stack2 = new Stack<>();
    public CQueue() {
    }
    public void appendTail(int value) {
        stack1.push(value);
    }
    public int deleteHead() {
        if (stack2.isEmpty()) {
            while (!stack1.isEmpty()) {
                stack2.push(stack1.pop());
            }
            if (stack2.isEmpty()) {
                return -1;
            }
        }
        return stack2.pop();
    }
}
// 解决方案(2)
class CQueue {
    LinkedList<Integer> A, B;
    public CQueue() {
        A = new LinkedList<Integer>();
        B = new LinkedList<Integer>();
    }
    public void appendTail(int value) {
        A.addLast(value);
    }
    public int deleteHead() {
        if(!B.isEmpty()) return B.removeLast();
        if(A.isEmpty()) return -1;
        while(!A.isEmpty())
            B.addLast(A.removeLast());
        return B.removeLast();
    }
}
/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue obj = new CQueue();
 * obj.appendTail(value);
 * int param_2 = obj.deleteHead();
 */

class CQueue {
public:
    stack<int> A, B;
    CQueue() {}
    void appendTail(int value) {
        A.push(value);
    }
    int deleteHead() {
        if(!B.empty()) {
            int tmp = B.top();
            B.pop();
            return tmp;
        }
        if(A.empty()) return -1;
        while(!A.empty()) {
            int tmp = A.top();
            A.pop();
            B.push(tmp);
        }
        int tmp = B.top();
        B.pop();
        return tmp;
    }
};