คอฟฟี่เบรค #162. การนำสแต็กไปใช้โดยใช้คิว วิธีการเรียนคณิตศาสตร์ Java

การใช้สแต็กโดยใช้คิว

["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]

MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // возвращает 2
myStack.pop(); // возвращает 2
myStack.empty(); // возвращает False

การแก้ปัญหา

ตัวเลือกแรก

static class MyStack {
  private Queue<Integer> current;
  private Queue<Integer> tmp;

  public MyStack() {
    current = new ArrayDeque<>();
    tmp = new ArrayDeque<>();
  }

public void push(int x) {
  current.add(x);
}

public int pop() {
  if (current.isEmpty()){
    return -1;
  }
  int size = current.size();
  for (int i = 0; i < size - 1; i ++){
    tmp.add(current.poll());
  }
  int ret = current.poll();
  current = tmp;
  return ret;
}

public int top() {
  if (current.isEmpty()){
    return -1;
  }
  int size = current.size();
  for (int i = 0; i < size - 1; i ++){
    tmp.add(current.poll());
  }
  int ret = current.peek();
  tmp.add(current.poll());
  current = tmp;
  return ret;
}

public boolean empty() {
  return current.isEmpty();
}

วิธีแก้ปัญหาที่สอง

static class MyStack {

  private Queue<Integer> current;

  public MyStack2() {
    current = new ArrayDeque<>();
  }
}

public void push(int x) {
  current.add(x);
  int size = current.size();

  for (int i = 0; i < size-1; i ++){
    current.add(current.poll());
  }
}

public int pop() {
  return current.poll();
}

public int top() {
  return current.peek();
}

public boolean empty() {
  return current.isEmpty();
}

วิธีการเรียนคณิตศาสตร์ Java

System.out.println(Math.max(5,3));
OUTPUT: 5

System.out.println(Math.sqrt(4));
OUTPUT: 2.0

System.out.println(Math.random());
OUTPUT: 0.8685304957692445

System.out.println(Math.abs(-4));
OUTPUT: 4
System.out.println(Math.abs(4));
OUTPUT: 4
System.out.println(Math.abs(0));
OUTPUT: 0

System.out.println(Math.floor(-1.2));
OUTPUT: -2.0
System.out.println(Math.floor(1.2));
OUTPUT: 2.0