剑指 Offer 09. 用两个栈实现队列

原题链接：剑指 Offer 09. 用两个栈实现队列

 

solution:
 

class CQueue {
public:
    stack<int> stk_i;
    stack<int> stk_o;
    CQueue() {

    }
    
    void appendTail(int value) {
        stk_i.push(value);
    }
    
    int deleteHead() {
        if(stk_i.empty() && stk_o.empty()) return -1;   //两个栈都为空,返回-1
        if(!stk_o.empty()) {    //出队栈不为空，直接返回
            int res = stk_o.top();
            stk_o.pop();
            return res;
        }
        else {
            while(!stk_i.empty()) {
                stk_o.push(stk_i.top());
                stk_i.pop();
            }
            int res = stk_o.top();
            stk_o.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();
 */