剑指 Offer 09. 用两个栈实现队列

题目链接

09. 用两个栈实现队列

思路分析

用两个栈实现队列，首先把1->2然后逐个弹出顶端元素。

class CQueue {
public:
    stack<int> stack1, stack2;
    CQueue() {

    }
    
    void appendTail(int value) {
        stack1.push(value);
    }
    
    int deleteHead() {
        std::ios::sync_with_stdio(false);
        if(stack1.empty() && stack2.empty()) return -1;
        if(!stack2.empty()){
            int tmp = stack2.top();
            stack2.pop();
            return tmp;
        }
        while(!stack1.empty()){
            int tmp = stack1.top();
            stack1.pop();
            stack2.push(tmp);
        }
        int res = stack2.top();
        stack2.pop();
        return res;
    }
};

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue* obj = new CQueue();
 * obj->appendTail(value);
 * int param_2 = obj->deleteHead();
 */