题解 | #用两个栈实现队列#

class Solution
{
public:
    void push(int node) {
	  //进栈入in栈
        stack1.push(node);
        
    }

    int pop() {
        int res;
        if(stack1.empty()&&stack2.empty())
            return -1;
		//如果out栈为空，将in栈内的数据全部放入out栈，此时out栈栈顶即为队首元素
        if(stack2.empty()){
            while(!stack1.empty()){
                stack2.push(stack1.top());
                stack1.pop();
            }
        }
	  //如果out栈不为空，直接out栈栈顶初战即可
        if(!stack2.empty()){
            res=stack2.top();
            stack2.pop();
            return res;
        }    
    return 0;
    }

private:
    stack<int> stack1; //in栈
    stack<int> stack2;  //out栈
};