LeetCode-Solutions-in-Cpp17

Solutions to high-frequency interview questions of LeetCode in C++17, taking into account both efficiency and comprehensibility.

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• 需要取第一个压入栈的元素时，将第一个栈的元素全倒入第二个栈，第二个栈中越靠近栈顶的就是越早入栈的元素。后续只需要取第二个栈元素，直到第二个栈为空时，再将第一个栈的元素全倒入第二个栈

class MyQueue {
 public:
  /** Initialize your data structure here. */
  MyQueue() {}

  /** Push element x to the back of queue. */
  void push(int x) { a.emplace(x); }

  /** Removes the element from in front of queue and returns that element. */
  int pop() {
    if (std::empty(b)) {
      while (!std::empty(a)) {
        int t = a.top();
        a.pop();
        b.emplace(t);
      }
    }
    int res = b.top();
    b.pop();
    return res;
  }

  /** Get the front element. */
  int peek() {
    if (std::empty(b)) {
      while (!std::empty(a)) {
        int t = a.top();
        a.pop();
        b.emplace(t);
      }
    }
    return b.top();
  }

  /** Returns whether the queue is empty. */
  bool empty() { return std::empty(a) && std::empty(b); }

 private:
  stack<int> a;
  stack<int> b;
};