Common methods of confusing stacks, one-way queues, and two-way queues

1. Use of stack

• Example:

      Deque<Integer> stack = new LinkedList<Integer>();
      stack.push(1);
      stack.push(3);
      stack.push(2);
      System.out.println(stack.size()); // 3
      System.out.println(stack.isEmpty());  // false
      stack.pop();
      System.out.println(stack.peek()); // 3
  

• Summarize:
  • Construction method:Deque<Integer> stack = new LinkedList<Integer>();
  • Member methods:
    • push: Add elements to the top of the stack
    • pop: Get and delete the top element of the stack
    • peek: Get but not delete the top element of the stack

2. Use of queues

• Example:

      Queue<Integer> queue = new LinkedList<Integer>();
      queue.offer(1);
      queue.offer(3);
      queue.offer(2);
      System.out.println(queue.size());   // 3
      System.out.println(queue.isEmpty()); // false
      System.out.println(queue.peek());   // 1
      queue.poll();
      System.out.println(queue.peek());   // 3
      ```
  

• Summarize:
  • Construction method:Queue<Integer> queue = new LinkedList<Integer>();
  • Member methods:
    • offer: Insert element to the end of the queue
    • poll: Get and delete the head element
    • peek: Get but not delete the head element

3. Use of two-way queue

• Construction method:Deque<Integer> stack = new LinkedList<Integer>();
• Member methods: All the above member methods can be used, so we can just use the deque as a queue or stack
  • Methods corresponding to queues
    • offer - offerLast
    • poll-pollFirst
    • peek-peekFirst
  • Methods corresponding to the stack
    • push-offerFirst
    • pop-pollFirst
    • peek-peekFirst