Recently, we are gnawing at data structure and algorithm. Welcome to communicate.

1.3.14: implement queue (FIFO) with variable length array

• Implementation of data structure ResizingArrayQueueOfStrings:

public class ResizingArrayQueueOfStrings {
	String[] arr;
	int N; 

	public ResizingArrayQueueOfStrings(int cap) {
		arr = new String[cap];
	}

	public void queue(String str) {
		if (N + 1 == arr.length) 
			resize(arr.length * 2);
		for (int i = N; i >= 0; i--) {
			arr[i + 1] = arr[i];
		}
		arr[0] = str;
		N++;
	}

	public String dequeue() {
		String s = arr[--N];
		if (N > 0 && N == arr.length / 4)
			resize(arr.length / 2);
		return s;
	}

	private void resize(int max) {
		String[] arrnew = new String[max];
		for (int i = 0; i <= N; i++) {
			arrnew[i] = arr[i];
		}
		arr = arrnew;
	
	}
	
	public boolean isEmpty(){
		return N == 0;
	}
	public int size(){
		return N;
	}
}

• client code

public class Ex1_3_14_Client {

	public static void main(String[] args) {
		ResizingArrayQueueOfStrings qos = new ResizingArrayQueueOfStrings(5);
		qos.queue("Baba ");
		qos.queue("black ");
		System.out.println("size1:"+qos.size());
		qos.queue("sheep ");
		qos.queue("have ");
		System.out.println("size2:"+qos.size());
		qos.queue("you ");
		qos.queue("any ");
		qos.queue("wood ");
		qos.queue("?");
		System.out.println("size3:"+qos.size());
		
		String s = "";
		while (!qos.isEmpty()) {
			s += qos.dequeue();			
		}
		System.out.println(s);		
	}
}

• Test results:

size1:2
size2:4
size3:8
Baba black sheep have you any wood ?

Baba black sheep have you any wood~

1.3.19: add a method to the stack based on the linked list, so that it can carry out "stack pressing" at the head and tail, and "spring stack" at the head and tail, and return the pop-up elements:

• Implementation of data structure MyLinkedlist:

public class MyLinkedlist<Item> {
	private int N;
	private Node first;
	private Node last;
	
	
	private class Node{
		Node next;
		Item item;
	}
	
	public void push(Item item){
		Node oldfirst = first;
		first = new Node();
		first.item = item;
		if (N == 0){
			first.next = null;
			last = first;
		}
		else
			first.next = oldfirst;
		N++;		
	}
		
	public void pushBottom(Item item) {
		Node oldlast = last;
		last = new Node();
		last.item = item;
		last.next = null;
		if (N == 0)
			first = last;
		else 
			oldlast.next = last;
		N++;
	}
	
	public Item pop(){
		Item item = first.item;
		first = first.next;
		N--;
		return item;
	}
	
	public Item popBottom(){
		Item item  = last.item;
		Node temp = first;
		for (int i = 1; i < N-1; i++) {
			temp = temp.next;       			// Node n-1 
		}
		last = temp;
		last.next = null;
		N--;
		return item;
	}
	
	public int size(){
		return N;
	}
}

• client code:

public class Ex1_3_19 {

	public static void main(String[] args) {
		MyLinkedlist<String> mll = new MyLinkedlist<>();
		mll.push("wood ");
		mll.push("any ");
		mll.push("you ");
		mll.push("have ");
		mll.pushBottom("? ");
		
		String str = "";
		int len = mll.size();
		for (int i = 0; i < len; i++) {
			str += mll.popBottom();
//              str += mll.pop();
		}
		System.out.println(str);
	}
}

• Test results:

popBottom:
? wood any you have 

pop:
have you any wood ?