1.3.42

question:

Copy a stack. Create a new constructor for the linked-list implementatiion of Stack so that
Stack<Item> t = new Stack<Item>(s);
makes t a reference to a new and independent copy of stack s.

answer:

//借用一个中转栈temp来进行复制

import edu.princeton.cs.algs4.*;

public class CopyStack<Item>
{
    private class Node
    {
        Item item;
        Node next;
    }
    
    private Node top;
    private int N;
    
    public CopyStack()
    {
        top = null;
        N = 0;
    }
    
    public CopyStack(CopyStack<Item> stack)
    {
        CopyStack<Item> temp = new CopyStack<Item>();//主要是用这个temp转换一下
        while(!stack.isEmpty())
        {
            Item item = stack.pop();
            temp.push(item);
        }
        while(!temp.isEmpty())
        {
            Item item = temp.pop();
            this.push(item);
            stack.push(item);
        }
    }
    
    public boolean isEmpty()
    {
        return N == 0;
    }
        
    public void push(Item item)
    {
        Node node = new Node();
        node.item = item;
        node.next = null;
        if(N == 0)
        {
            top = node;
            N++;
            return;
        }
        N++;
        node.next = top;
        top = node;
    }
    
    public Item pop()
    {
        if(N == 0)
        {
            return null;
        }
        N--;
        Item item = top.item;
        top = top.next;
        return item;
    }
    
    public static void main(String[] args)
    {
        CopyStack<String> s1 = new CopyStack<String>();
        s1.push("c");
        s1.push("j");
        s1.push("w");
        CopyStack<String> s2 = new CopyStack<String>(s1);
        for(int i = 0; i < 3; i++)
        {
            StdOut.print("s1\t" + s1.pop() + "\ts2\t" + s2.pop() + "\n");
        }
    }
}

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