Programming Assignment2 - Deque and Randomized Queues Review

Assignment Specification

課程筆記

Subtext: Modular Programming

• Stacks and Queues are fundamental data types
  • Value: collection of objects
  • Basic Operation: insert, remove, iterate.
  • Difference: which item do we move? -> Stack: LIFO(last in first out) Queue: FIFO(first in first out)
• Client, implementation, interface
  • Client: program using operations defined in interface
  • Implementation: actual code implementing operations
  • Interface: description of data type, basic operations

Stack Programming API:

public class StackOfStrings
StackOfStrings() //create an empty stack
void push(String item)  //insert a new string onto stack
 

String pop() //remove and return the string most recently added
boolean isEmpty()  //is the stack empty?

linked-list implementation

//Attention: Stack have only one exit -> only one pointer is enough
/*Corner Cases:
    client add a null item -> IllegalArgumentException
    remove() from empty stack -> NoSuchElementException
 

*/
public class StackOfStrings {
    private Node first;
    private class Node {
        String item;
        Node next;
    }
    
    public boolean isEmpty() {
        return first == null;
    }
    
    public StackOfStrings {
        Node first = null;
    }

    public void push(String item) {
        //Improve: add exception to deal with invalid operation
        Node oldfirst = first;
        first = new Node(); //Attention: must craete a new instance here
        first.item = item;
        first.next = oldfirst;
    }

    public String pop() {
        String item = first.item;
        first = first.next;
        return item;
    }

在寫代碼的過程當中，心裏需要有轉換角色的意識，當你在實現一個API的時候，需要考慮的是
* 實現某個方法所要使用的數據結構，
* 調用方法 or 自己寫方法，
* API的性能要求 -> 使用哪種算法可以滿足要求 查找，插入，刪除 時間 + 空間

Stack的鏈表實現
Stack的數組實現（resize array)

Queue的鏈表實現
Queue的數組實現（resize array)

對於雙向隊列的理解有誤，導致錯誤實現。
雙向對別不應當是兩個隊列的水平疊加，見figure 1

作業總結：

1. 對於文件的讀寫基本操作命令不夠熟悉
2. 對於問題的定義 出現了沒有搞清楚題目要求的現象，包括Deque的基本操作 以及Permutation 類當中，應當是讀取全部數據，輸出k個數據，而不是讀取k個數據，輸出全部數據的問題

PrincetonAlgorithm I - Assignment2 Deques and Randomized Queues