data_structures_free

net/datastructures/NodeStack.java

@@ -0,0 +1,116 @@
+package net.datastructures;
+/**
+ * Implementation of the stack ADT by means of a singly linked list.
+ *   
+ * @author Natasha Gelfand
+ * @author Roberto Tamassia
+ * @see Node
+ */
+ 
+//begin#fragment NodeStack
+public class NodeStack<E> implements Stack<E> {
+  protected Node<E> top;	// reference to the head node
+  protected int size;		// number of elements in the stack
+//end#fragment NodeStack
+  /** Creates an empty stack. */
+//begin#fragment NodeStack
+  public NodeStack() {	// constructs an empty stack
+    top = null;
+    size = 0;
+  }
+  public int size() { return size; }
+  public boolean isEmpty() {
+    if (top == null) return true;
+    return false;
+  }
+  public void push(E elem) {
+    Node<E> v = new Node<E>(elem, top);	// create and link-in a new node
+    top = v;
+    size++;
+  }
+  public E top() throws EmptyStackException {
+    if (isEmpty()) throw new EmptyStackException("Stack is empty.");
+    return top.getElement();
+  }
+  public E pop() throws EmptyStackException {
+    if (isEmpty()) throw new EmptyStackException("Stack is empty.");
+    E temp = top.getElement();
+    top = top.getNext();	// link-out the former top node
+    size--;
+    return temp;
+  }
+//end#fragment NodeStack
+
+
+ /**
+  * Returns a string representation of the stack as a list of elements,
+  * with the top element at the end: [ ... , prev, top ].
+  * This method runs in O(n) time, where n is the size of the stack.
+  * @return textual representation of the stack.
+  */
+  public String toString() {
+    String s;
+    Node<E> cur = null;
+    s = "[";
+    int n = size();
+    if (n > 0) {
+      cur = top;
+      s += cur.getElement();
+    }
+    if (n > 1)
+      for (int i = 1; i <= n-1; i++) {
+	cur = cur.getNext();
+	s += ", " + cur.getElement();
+      }
+    s += "]";
+    return s;
+  }
+
+ /**
+  * Prints information about an operation and the stack.
+  * @param op operation performed
+  * @param element element returned by the operation
+  * @return information about the operation performed, the element
+  * returned by the operation and the content of the stack after 
+  * the operation.
+  */ 
+  public static void status(Stack S, String op, Object element) {
+    System.out.println("---------------------------------");
+    System.out.println(op);
+    System.out.println("Returned: " + element);
+    String emptyStatus;
+    if (S.isEmpty())
+      emptyStatus = "empty";
+    else
+      emptyStatus = "not empty";
+    System.out.println("size = " + S.size() + ", " + emptyStatus);
+    System.out.println("Stack: " + S);
+  }
+
+ /**
+  * Test program that performs a series of operations on on a stack and
+  * prints the operation performed, the returned element and the
+  * content of the stack after each operation.
+  */
+  public static void main(String[] args) {
+    Object o;
+    Stack<Integer> A = new NodeStack<Integer>();
+    status (A, "New empty stack", null);
+    A.push(5);
+    status (A, "push(5)", null);
+    A.push(3);
+    status (A, "push(3)", null);
+    A.push(7);
+    status (A, "push(7)", null);
+    o = A.pop();
+    status (A, "pop()", o);
+    A.push(9);
+    status (A, "push(9)", null);
+    o = A.pop();
+    status (A, "pop()", o);
+    o = o = A.top();
+    status (A, "top()", o);
+  }
+//begin#fragment NodeStack
+}
+//end#fragment NodeStack