算法Sedgewick第四版-第1章基础-008一用数组实现栈(泛型、可变大小)

 package algorithms.ADT;

 /******************************************************************************
  *  Compilation:  javac FixedCapacityStackOfStrings.java
  *  Execution:    java FixedCapacityStackOfStrings
  *  Dependencies: StdIn.java StdOut.java
  *
  *  Stack of strings implementation with a fixed-size array.
  *
  *  % more tobe.txt
  *  to be or not to - be - - that - - - is
  *
  *  % java FixedCapacityStackOfStrings 5 < tobe.txt
  *  to be not that or be
  *
  *  Remark:  bare-bones implementation. Does not do repeated
  *  doubling or null out empty array entries to avoid loitering.
  *
  ******************************************************************************/

 import java.util.Iterator;
 import java.util.NoSuchElementException;

 import algorithms.util.StdIn;
 import algorithms.util.StdOut;

 public class FixedCapacityStackOfStrings implements Iterable<String> {
     private String[] a;  // holds the items
     private int N;       // number of items in stack

     // create an empty stack with given capacity
     public FixedCapacityStackOfStrings(int capacity) {
         a = new String[capacity];
         N = 0;
     }

     public boolean isEmpty()            {  return N == 0;                    }
     public boolean isFull()             {  return N == a.length;             }
     public void push(String item)       {  a[N++] = item;                    }
     public String pop()                 {  return a[--N];                    }
     public String peek()                {  return a[N-1];                    }
     public Iterator<String> iterator()  { return new ReverseArrayIterator(); }

     public class ReverseArrayIterator implements Iterator<String> {
         private int i = N-1;

         public boolean hasNext() {
             return i >= 0;
         }

         public String next() {
             if (!hasNext()) throw new NoSuchElementException();
             return a[i--];
         }

         public void remove() {
             throw new UnsupportedOperationException();
         }
     }

     public static void main(String[] args) {
         int max = Integer.parseInt(args[0]);
         FixedCapacityStackOfStrings stack = new FixedCapacityStackOfStrings(max);
         while (!StdIn.isEmpty()) {
             String item = StdIn.readString();
             if (!item.equals("-")) stack.push(item);
             else if (stack.isEmpty())  StdOut.println("BAD INPUT");
             else                       StdOut.print(stack.pop() + " ");
         }
         StdOut.println();

         // print what's left on the stack
         StdOut.print("Left on stack: ");
         for (String s : stack) {
             StdOut.print(s + " ");
         }
         StdOut.println();
     }
 } 

用泛型的

 package algorithms.ADT;

 /******************************************************************************
  *  Compilation:  javac FixedCapacityStack.java
  *  Execution:    java FixedCapacityStack
  *  Dependencies: StdIn.java StdOut.java
  *
  *  Generic stack implementation with a fixed-size array.
  *
  *  % more tobe.txt
  *  to be or not to - be - - that - - - is
  *
  *  % java FixedCapacityStack 5 < tobe.txt
  *  to be not that or be
  *
  *  Remark:  bare-bones implementation. Does not do repeated
  *  doubling or null out empty array entries to avoid loitering.
  *
  ******************************************************************************/

 import java.util.Iterator;
 import java.util.NoSuchElementException;

 import algorithms.util.StdIn;
 import algorithms.util.StdOut;

 public class FixedCapacityStack<Item> implements Iterable<Item> {
     private Item[] a;    // holds the items
     private int N;       // number of items in stack

     // create an empty stack with given capacity
     public FixedCapacityStack(int capacity) {
         a = (Item[]) new Object[capacity];   // no generic array creation
         N = 0;
     }

     public boolean isEmpty()          {  return N == 0;                    }
     public void push(Item item)       {  a[N++] = item;                    }
     public Item pop()                 {  return a[--N];                    }
     public Iterator<Item> iterator()  { return new ReverseArrayIterator(); }

     public class ReverseArrayIterator implements Iterator<Item> {
         private int i = N-1;

         public boolean hasNext() {
             return i >= 0;
         }

         public Item next() {
             if (!hasNext()) throw new NoSuchElementException();
             return a[i--];
         }

         public void remove() {
             throw new UnsupportedOperationException();
         }
     }

     public static void main(String[] args) {
         int max = Integer.parseInt(args[0]);
         FixedCapacityStack<String> stack = new FixedCapacityStack<String>(max);
         while (!StdIn.isEmpty()) {
             String item = StdIn.readString();
             if (!item.equals("-")) stack.push(item);
             else if (stack.isEmpty())  StdOut.println("BAD INPUT");
             else                       StdOut.print(stack.pop() + " ");
         }
         StdOut.println();

         // print what's left on the stack
         StdOut.print("Left on stack: ");
         for (String s : stack) {
             StdOut.print(s + " ");
         }
         StdOut.println();
     }
 } 

可变大小的

 package algorithms.ADT;

 /******************************************************************************
  *  Compilation:  javac ResizingArrayStack.java
  *  Execution:    java ResizingArrayStack < input.txt
  *  Dependencies: StdIn.java StdOut.java
  *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
  *
  *  Stack implementation with a resizing array.
  *
  *  % more tobe.txt
  *  to be or not to - be - - that - - - is
  *
  *  % java ResizingArrayStack < tobe.txt
  *  to be not that or be (2 left on stack)
  *
  ******************************************************************************/

 import java.util.Iterator;
 import java.util.NoSuchElementException;

 import algorithms.util.StdIn;
 import algorithms.util.StdOut;

 /**
  *  The <tt>ResizingArrayStack</tt> class represents a last-in-first-out (LIFO) stack
  *  of generic items.
  *  It supports the usual <em>push</em> and <em>pop</em> operations, along with methods
  *  for peeking at the top item, testing if the stack is empty, and iterating through
  *  the items in LIFO order.
  *  <p>
  *  This implementation uses a resizing array, which double the underlying array
  *  when it is full and halves the underlying array when it is one-quarter full.
  *  The <em>push</em> and <em>pop</em> operations take constant amortized time.
  *  The <em>size</em>, <em>peek</em>, and <em>is-empty</em> operations takes
  *  constant time in the worst case.
  *  <p>
  *  For additional documentation,
  *  see <a href="http://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
  *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
  *
  *  @author Robert Sedgewick
  *  @author Kevin Wayne
  */
 public class ResizingArrayStack<Item> implements Iterable<Item> {
     private Item[] a;         // array of items
     private int N;            // number of elements on stack

     /**
      * Initializes an empty stack.
      */
     public ResizingArrayStack() {
         a = (Item[]) new Object[2];
         N = 0;
     }

     /**
      * Is this stack empty?
      * @return true if this stack is empty; false otherwise
      */
     public boolean isEmpty() {
         return N == 0;
     }

     /**
      * Returns the number of items in the stack.
      * @return the number of items in the stack
      */
     public int size() {
         return N;
     }

     // resize the underlying array holding the elements
     private void resize(int capacity) {
         assert capacity >= N;
         Item[] temp = (Item[]) new Object[capacity];
         for (int i = 0; i < N; i++) {
             temp[i] = a[i];
         }
         a = temp;
     }

     /**
      * Adds the item to this stack.
      * @param item the item to add
      */
     public void push(Item item) {
         if (N == a.length) resize(2*a.length);    // double size of array if necessary
         a[N++] = item;                            // add item
     }

     /**
      * Removes and returns the item most recently added to this stack.
      * @return the item most recently added
      * @throws java.util.NoSuchElementException if this stack is empty
      */
     public Item pop() {
         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
         Item item = a[N-1];
         a[N-1] = null;                              // to avoid loitering
         N--;
         // shrink size of array if necessary
         if (N > 0 && N == a.length/4) resize(a.length/2);
         return item;
     }

     /**
      * Returns (but does not remove) the item most recently added to this stack.
      * @return the item most recently added to this stack
      * @throws java.util.NoSuchElementException if this stack is empty
      */
     public Item peek() {
         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
         return a[N-1];
     }

     /**
      * Returns an iterator to this stack that iterates through the items in LIFO order.
      * @return an iterator to this stack that iterates through the items in LIFO order.
      */
     public Iterator<Item> iterator() {
         return new ReverseArrayIterator();
     }

     // an iterator, doesn't implement remove() since it's optional
     private class ReverseArrayIterator implements Iterator<Item> {
         private int i;

         public ReverseArrayIterator() {
             i = N-1;
         }

         public boolean hasNext() {
             return i >= 0;
         }

         public void remove() {
             throw new UnsupportedOperationException();
         }

         public Item next() {
             if (!hasNext()) throw new NoSuchElementException();
             return a[i--];
         }
     }

     /**
      * Unit tests the <tt>Stack</tt> data type.
      */
     public static void main(String[] args) {
         ResizingArrayStack<String> s = new ResizingArrayStack<String>();
         while (!StdIn.isEmpty()) {
             String item = StdIn.readString();
             if (!item.equals("-")) s.push(item);
             else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
         }
         StdOut.println("(" + s.size() + " left on stack)");
     }
 }