剑指offer04:用两个栈实现队列

class Solution
{
public:
    void push(int node) {
        stack1.push(node);
    }

    int pop() {
        int pdata = 0;
        if(!stack2.empty()){
            pdata = stack2.top();
            stack2.pop();
        }
        else{
            if(!stack1.empty()){
                while(!stack1.empty()){
                    stack2.push(stack1.top());
                    stack1.pop();
                }
                pdata = stack2.top();
                stack2.pop();
            }
            else{
                return -1;
            }
        }
        return pdata;
    }

private:
    stack<int> stack1;
    stack<int> stack2;
};