力扣1670.设计前中后队列

力扣1670.设计前中后队列

• 两个双端队列

• 

  • 始终保证right.size() >= left.size()
  • 向中间插入时如果一样长 就插入right
  • 如果right长就插入left

  class FrontMiddleBackQueue {
  private:
      deque<int> left;
      deque<int> right;
      //保证left.size() + 1 >= right.size() >= left.size()
      void banlance()
      {
          if(left.size() > right.size())
          {
              right.push_front(left.back());
              left.pop_back();
          }
          else if(right.size() > left.size() + 1)
          {
              left.push_back(right.front());
              right.pop_front();
          }
      }
  public:
      
      FrontMiddleBackQueue() {
  
      }
      
      void pushFront(int val) {
          left.push_front(val);
          banlance();
      }
      
      void pushMiddle(int val) {
          if(left.size() < right.size())
              left.push_back(val);
          else
              right.push_front(val);
      }
      
      void pushBack(int val) {
          right.push_back(val);
          banlance();
      }
      
      int popFront() {
          if(right.empty())
              return -1;
          int val;
          if(left.empty())
          {
              val = right.front();
              right.pop_front();
          }
          else
          {
              val = left.front();
              left.pop_front();
          }
          banlance();
          return val;
      }
      
      int popMiddle() {
          if(right.empty())
              return -1;
          int val;
          if(left.size() == right.size())
          {
              val = left.back();
              left.pop_back();
          }
          else
          {
              val = right.front();
              right.pop_front();
          }
          return val;
      }
      
      int popBack() {
          if(right.empty())
              return -1;
          int val = right.back();
          right.pop_back();
          banlance();
          return val;
      }
  };