{面试题7: 用两个栈实现队列}

From 剑指Offer 何海涛 著

#include <iostream>
#include <stack>
#include <exception>


template<typename T>
class CQueue {
    public:
        CQueue(void);
        ~CQueue(void);

        void appendTail(const T& node);
        T deleteHead();
        
    private:
        std::stack<T> stack1;
        std::stack<T> stack2;

};

template<typename T>
CQueue<T>::CQueue() {
    
}
template<typename T>
CQueue<T>::~CQueue() {
    
}

template<typename T>
void CQueue<T>::appendTail(const T& node) {
    stack1.push(node);
}

template<typename T>
T CQueue<T>::deleteHead() {
    if(stack2.empty()) {
        while(!stack1.empty()) {
            T& t = stack1.top();
            stack2.push(t);
            stack1.pop();
        }
        if(stack2.empty()) {
            throw std::exception();
        }
    }
    T t = stack2.top();
    stack2.pop();
    return t;
} 

 测试集:

template<typename T>
void test(const T& actual, const T& expected) {
    std::cout << std::boolalpha << (actual == expected) << std::endl;
}

int main(int argc, char* argv[]) {
    CQueue<char> queue;
    queue.appendTail('a');
    queue.appendTail('b');
    queue.appendTail('c');
    
    test(queue.deleteHead(), 'a');
    queue.appendTail('d');
    test(queue.deleteHead(), 'b');
    test(queue.deleteHead(), 'c');
    test(queue.deleteHead(), 'd');
    try {
        queue.deleteHead();
    } catch(std::exception &e) {
        std::cout << "true" << std::endl;
    }
    
    return 0;
}