1670. Design Front Middle Back Queue.md

1670. Design Front Middle Back Queue

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the third one in Biweekly Contest 40.

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Difficulty : Medium

Related Topics : Linked List、Design、Dequeue

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Design a queue that supports push and pop operations in the front, middle, and back.

Implement the FrontMiddleBack class:

• FrontMiddleBack() Initializes the queue.
• void pushFront(int val) Adds val to the front of the queue.
• void pushMiddle(int val) Adds val to the middle of the queue.
• void pushBack(int val) Adds val to the back of the queue.
• int popFront() Removes the front element of the queue and returns it. If the queue is empty, return -1.
• int popMiddle() Removes the middle element of the queue and returns it. If the queue is empty, return -1.
• int popBack() Removes the back element of the queue and returns it. If the queue is empty, return -1.

Notice that when there are two middle position choices, the operation is performed on the frontmost middle position choice. For example:

• Pushing 6 into the middle of [1, 2, 3, 4, 5] results in [1, 2, 6, 3, 4, 5].
• Popping the middle from [1, 2, 3, 4, 5, 6] returns 3 and results in [1, 2, 4, 5, 6].

Example 1:

Input:
["FrontMiddleBackQueue", "pushFront", "pushBack", "pushMiddle", "pushMiddle", "popFront", "popMiddle", "popMiddle", "popBack", "popFront"]
[[], [1], [2], [3], [4], [], [], [], [], []]
Output:
[null, null, null, null, null, 1, 3, 4, 2, -1]

Explanation:
FrontMiddleBackQueue q = new FrontMiddleBackQueue();
q.pushFront(1);   // [1]
q.pushBack(2);    // [1, 2]
q.pushMiddle(3);  // [1, 3, 2]
q.pushMiddle(4);  // [1, 4, 3, 2]
q.popFront();     // return 1 -> [4, 3, 2]
q.popMiddle();    // return 3 -> [4, 2]
q.popMiddle();    // return 4 -> [2]
q.popBack();      // return 2 -> []
q.popFront();     // return -1 -> [] (The queue is empty)

Constraints:

• 1 <= val <= 10^9
• At most 1000 calls will be made to pushFront, pushMiddle, pushBack, popFront, popMiddle, and popBack.

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Solution

• mine
  • Java
    • Runtime: 7 ms, faster than 100.00%, Memory Usage: 39.5 MB, less than 100.00% of Java online submissions

      class FrontMiddleBackQueue {
          
          List<Integer> list;
      
          public FrontMiddleBackQueue() {
              list = new ArrayList<>();
          }
          
          public void pushFront(int val) {
              list.add(0, val);
          }
          
          public void pushMiddle(int val) {
              int size = list.size();
              list.add(size/ 2 , val);
          }
          
          public void pushBack(int val) {
              list.add(val);
          }
          
          public int popFront() {
              if(list.size() == 0) return -1;
              return list.remove(0);
          }
          
          public int popMiddle() {
              int size = list.size();
              if(size == 0) return -1;
              int index = 0;
              if(size % 2 == 0 && size > 0){
                  index = (size - 1) / 2;
              }else{
                  index = size / 2;
              }
              return list.remove(index);
          }
          
          public int popBack() {
              if(list.size() == 0) return -1;
              return list.remove(list.size() - 1);
          }
      }
      

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• the most votes

• Runtime: 7 ms, faster than 100.00%, Memory Usage: 39.5 MB, less than 100.00% of Java online submissions

  class FrontMiddleBackQueue {
      LinkedList<Integer> left, right;
      int size;
  
      public FrontMiddleBackQueue() {
          left = new LinkedList<>();
          right = new LinkedList<>();
          size = 0;
      }
  
      public void pushFront(int val) {
          left.addFirst(val);
          if (left.size() > right.size()) {
              right.addFirst(left.removeLast());
          }
          size++;
      }
  
      public void pushMiddle(int val) {
          if (left.size() == right.size()) {
              right.addFirst(val);
          } else {
              left.addLast(val);
          }
          size++;
      }
  
      public void pushBack(int val) {
          if (left.size() < right.size()) {
              left.addLast(right.removeFirst());
          }
          right.addLast(val);
          size++;
      }
  
      public int popFront() {
          if (size == 0) {
              return -1;
          }
          if (left.size() < right.size()) {
              left.addLast(right.removeFirst());
          }
          int val = left.removeFirst();
          size--;
          return val;
      }
  
      public int popMiddle() {
          if (size == 0) {
              return -1;
          }
          int val;
          if (left.size() == right.size()) {
              val = left.removeLast();
          } else {
              val = right.removeFirst();
          }
          size--;
          return val;
      }
  
      public int popBack() {
          if (size == 0) {
              return -1;
          }
          int val = right.removeLast();
          if (left.size() > right.size()) {
              right.addFirst(left.removeLast());
          }
          size--;
          return val;
      }
  }
  

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