queue&stack

Chapter1/Queue.java

@@ -0,0 +1,76 @@
+import edu.princeton.cs.introcs.StdOut;
+
+import java.util.Iterator;
+
+public class Queue<Item> implements Iterable<Item>
+{
+    private Node first;
+    private Node last;
+    private int N;
+    private class Node
+    {
+        Item item;
+        Node next;
+    }
+    public boolean isEmpty() {return first==null;}
+    public int size()   {return N;}
+    public void enqueue(Item item)
+    {
+//        last.next = new Node();
+//        last = last.next;
+//        last.item = item;
+//        N++;
+        Node oldlast = last;
+        last = new Node();
+        last.item = item;
+        last.next = null;
+        if(isEmpty())   first = last;
+        else            oldlast.next = last;
+        N++;
+    }
+    public Item dequeue()
+    {
+        Item item = first.item;
+        first = first.next;
+        if(isEmpty()) last = null;
+        N--;
+        return item;
+    }
+    public Iterator<Item> iterator()
+    {
+        return new ReverseArrayIterator();
+    }
+    private class ReverseArrayIterator implements Iterator<Item>
+    {
+        int i = 0;
+        Node nextnode = first;
+        @Override
+        public boolean hasNext() {
+            return i<N;
+        }
+
+        @Override
+        public Item next() {
+
+            if(i!=0)
+                nextnode = nextnode.next;
+            i++;
+            return nextnode.item;
+        }
+
+        @Override
+        public void remove() {
+
+        }
+    }
+
+    public static void main(String[] args)
+    {
+        Queue<Integer> q = new Queue<Integer>();
+        q.enqueue(1);
+        q.enqueue(2);
+        q.enqueue(5);
+        for(int i:q)
+            StdOut.println(i);
+    }
+}