在java中实现deque的问题 [英] Problems with implementing a deque in java

问题描述

抱歉，继续我在这里提出的问题：这里我正在尝试运行此方法从双面队列（deque）中删除一般值（EltType），但我不断收到错误，我调用insertFirst两次，并将值3插入数组两次，然后，当我运行removeFirst，它将打印出3一次，然后Null。有人可以帮我吗？

  class ArrayBasedDeque< EltType> {
 
 private final int CAPACITY = 10; 
私人产能; 
 private int end; 
 private EltType deque []; 
 
 public ArrayBasedDeque（）{
 this.capacity = CAPACITY; 
 deque =（EltType []）（new Object [capacity]）; 
} 
 
 
 public EltType removeFirst（）{
 EltType [] tempArray; 
 EltType返回= deque [0]; 
 tempArray =（EltType []）new Object [capacity]; 
 for（int i = 1; i< capacity; i ++）{
 tempArray [i-1] = deque [i]; 
} 
 deque = tempArray;返回
退货; 
} 
 
 
 public boolean isEmpty（）{
 return end == 0; 
} 
 
 public void insertFirst（EltType first）{
 if（！isEmpty（））{
 EltType [] tempArray; 
 tempArray =（EltType []）new Object [capacity + 1]; 
 for（int i = 0; i< deque.length; i ++）{
 tempArray [i + 1] = deque [i]; 
} 
 deque = tempArray; 
} 
 deque [0] =第一个; 
} 
 
} 
  

谢谢：）

解决方案

明显的问题是 end 永远不会改变。 isEmpty（）将始终返回 true 。现在让我们看看你的 insertFirst（）方法。

  public void insertFirst （EltType first）{
 if（！isEmpty（））{
 EltType [] tempArray; 
 tempArray =（EltType []）new Object [capacity + 1]; 
 for（int i = 0; i< deque.length; i ++）{
 tempArray [i + 1] = deque [i]; 
} 
 
 deque = tempArray; 
} 
 deque [0] =第一个; 
} 
  

知道 isEmpty（）总是返回 true 无论如何，这段代码有什么问题？

sorry, just following on from the question I had here : here I am trying to run this method to remove a generic value (EltType) from a double sided queue(deque), but I keep getting an error in that, I call insertFirst twice, and insert the value "3" into the array twice, then, when I run removeFirst, it will print out "3" once, and then "Null" thereafter. Would anyone be able to help me out please ?

class ArrayBasedDeque<EltType> {

  private final int CAPACITY = 10;
  private int capacity;
  private int end;
  private EltType deque[];  

  public ArrayBasedDeque() {
    this.capacity = CAPACITY;
    deque = (EltType[]) (new Object[capacity]);  
  } 


 public EltType removeFirst() {
    EltType[] tempArray;
    EltType returned = deque[0];
    tempArray = (EltType[]) new Object[capacity];
      for (int i=1;i<capacity;i++) {
        tempArray[i-1] = deque[i]; 
      }
      deque = tempArray;
    return returned;
  }


  public boolean isEmpty() {
    return end == 0;
  }

  public void insertFirst(EltType first) {
    if(!isEmpty()) {
    EltType[] tempArray;
    tempArray = (EltType[]) new Object[capacity+1];
    for (int i=0;i<deque.length;i++) {
      tempArray[i+1] = deque[i]; 
    }
    deque = tempArray; 
    }
   deque[0] = first;
  }

}

Thank you :)

解决方案

The big glaring issue is that end never changes. isEmpty() will always return true. Now let's look at your insertFirst() method.

public void insertFirst(EltType first) {
    if(!isEmpty()) {
        EltType[] tempArray;
        tempArray = (EltType[]) new Object[capacity+1];
        for (int i=0;i<deque.length;i++) {
            tempArray[i+1] = deque[i]; 
        }

        deque = tempArray; 
    } 
    deque[0] = first;
}

Knowing that isEmpty() always returns true no matter what, what is the problem with this piece of code?

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