[剑指offer]面试题7：用两个栈实现队列

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

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

int res = stack2.top();
stack2.pop();
return res;
}

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