用两个栈实现队列

#include<iostream>
#include<stack>
#include<string>

using namespace std;
stack<int> stack1;
stack<int> stack2;

void Push(const int &node){                      //对stack1进行push操作
stack1.push(node);
}

int Pop(){                                        //将stack2进行pop操作
if(stack2.size() <= 0){
while(stack1.size() > 0){
int &data = stack1.top();
stack1.pop();
stack2.push(data);
}
}

if(stack2.size() == 0){
return -1;
}

int head = stack2.top();
stack2.pop();

return head;
}

int main(){
long num;
string str;
cin >> num;

while(num-- > 0){
cin>>str;
if(str == "PUSH"){
int x;
cin>>x;
Push(x);
}
else if(str == "POP"){
int ls = Pop();
if(ls < 0){
cout<<"-1"<<endl;
}else{
cout<<ls<<endl;
}
}
}
return 0;
}