Implement Queue using Stacks LeetCode solution in C++

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class MyQueue {
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 public:
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  stack<int> s1;
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  stack<int> s2;
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  MyQueue() {}
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  void push(int x) {
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    s1.push(x);
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  }
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  int pop() {
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    if (s1.empty() && s2.empty()) return -1;
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    while (s2.empty()) {
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      while (!s1.empty()) {
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        s2.push(s1.top());
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        s1.pop();
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      }
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    }
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    int x = s2.top();
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    s2.pop();
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    return x;
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  }
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  int peek() {
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    if (!s2.empty()) {
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      return s2.top();
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    } else {
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      while (!s1.empty()) {
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        int val = s1.top();
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        s2.push(val);
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        s1.pop();
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      }
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      return s2.top();
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    }
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  }
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  bool empty() {
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    if (s1.empty() && s2.empty()) {
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      return true;
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    }
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    return false;
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  }
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};
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/**
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 * Your MyQueue object will be instantiated and called as such:
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 * MyQueue* obj = new MyQueue();
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 * obj->push(x);
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 * int param_2 = obj->pop();
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 * int param_3 = obj->peek();
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 * bool param_4 = obj->empty();
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 */