剑指 Offer 09. 用两个栈实现队列

剑指 Offer 09. 用两个栈实现队列

思路：

一个栈用来辅助，另一个用来维护队列的值。

代码：

class CQueue {
public:
    CQueue() {

    }
    
    void appendTail(int value) {
        stk1.push(value);
    }
    
    int deleteHead() {
        if(stk1.empty()) return -1;
        while(stk1.size() != 1){
            stk2.push(stk1.top());
            stk1.pop();
        }
        int res = stk1.top();
        stk1.pop();
        while(stk2.size()) {
            stk1.push(stk2.top());
            stk2.pop();
        }
        return res;
    }
    stack<int> stk1;
    stack<int> stk2;
};

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