算法Sedgewick第四版-第1章基础-008一用数组实现固定长度的栈

 1 package algorithms.ADT;
 2 
 3 /******************************************************************************
 4  *  Compilation:  javac FixedCapacityStackOfStrings.java
 5  *  Execution:    java FixedCapacityStackOfStrings
 6  *  Dependencies: StdIn.java StdOut.java
 7  *  
 8  *  Stack of strings implementation with a fixed-size array.
 9  *
10  *  % more tobe.txt 
11  *  to be or not to - be - - that - - - is 
12  * 
13  *  % java FixedCapacityStackOfStrings 5 < tobe.txt 
14  *  to be not that or be
15  *
16  *  Remark:  bare-bones implementation. Does not do repeated
17  *  doubling or null out empty array entries to avoid loitering.
18  *
19  ******************************************************************************/
20 
21 import java.util.Iterator;
22 import java.util.NoSuchElementException;
23 
24 import algorithms.util.StdIn;
25 import algorithms.util.StdOut;
26 
27 public class FixedCapacityStackOfStrings implements Iterable<String> {
28     private String[] a;  // holds the items
29     private int N;       // number of items in stack
30 
31     // create an empty stack with given capacity
32     public FixedCapacityStackOfStrings(int capacity) {
33         a = new String[capacity];
34         N = 0;
35     }
36 
37     public boolean isEmpty()            {  return N == 0;                    }
38     public boolean isFull()             {  return N == a.length;             }
39     public void push(String item)       {  a[N++] = item;                    }
40     public String pop()                 {  return a[--N];                    }
41     public String peek()                {  return a[N-1];                    }
42     public Iterator<String> iterator()  { return new ReverseArrayIterator(); }
43 
44 
45     public class ReverseArrayIterator implements Iterator<String> {
46         private int i = N-1;
47 
48         public boolean hasNext() {
49             return i >= 0;
50         }
51 
52         public String next() { 
53             if (!hasNext()) throw new NoSuchElementException();
54             return a[i--];
55         }
56 
57         public void remove() {
58             throw new UnsupportedOperationException();
59         }
60     }
61 
62 
63     public static void main(String[] args) {
64         int max = Integer.parseInt(args[0]);
65         FixedCapacityStackOfStrings stack = new FixedCapacityStackOfStrings(max);
66         while (!StdIn.isEmpty()) {
67             String item = StdIn.readString();
68             if (!item.equals("-")) stack.push(item); 
69             else if (stack.isEmpty())  StdOut.println("BAD INPUT"); 
70             else                       StdOut.print(stack.pop() + " ");
71         }
72         StdOut.println();
73 
74         // print what‘s left on the stack
75         StdOut.print("Left on stack: ");
76         for (String s : stack) {
77             StdOut.print(s + " ");
78         }
79         StdOut.println();
80     } 
81 } 

 1 package algorithms.ADT;
 2 
 3 /******************************************************************************
 4  *  Compilation:  javac FixedCapacityStack.java
 5  *  Execution:    java FixedCapacityStack
 6  *  Dependencies: StdIn.java StdOut.java
 7  *  
 8  *  Generic stack implementation with a fixed-size array.
 9  *
10  *  % more tobe.txt 
11  *  to be or not to - be - - that - - - is 
12  * 
13  *  % java FixedCapacityStack 5 < tobe.txt 
14  *  to be not that or be
15  *
16  *  Remark:  bare-bones implementation. Does not do repeated
17  *  doubling or null out empty array entries to avoid loitering.
18  *
19  ******************************************************************************/
20 
21 import java.util.Iterator;
22 import java.util.NoSuchElementException;
23 
24 import algorithms.util.StdIn;
25 import algorithms.util.StdOut;
26 
27 public class FixedCapacityStack<Item> implements Iterable<Item> {
28     private Item[] a;    // holds the items
29     private int N;       // number of items in stack
30 
31     // create an empty stack with given capacity
32     public FixedCapacityStack(int capacity) {
33         a = (Item[]) new Object[capacity];   // no generic array creation
34         N = 0;
35     }
36 
37     public boolean isEmpty()          {  return N == 0;                    }
38     public void push(Item item)       {  a[N++] = item;                    }
39     public Item pop()                 {  return a[--N];                    }
40     public Iterator<Item> iterator()  { return new ReverseArrayIterator(); }
41 
42 
43     public class ReverseArrayIterator implements Iterator<Item> {
44         private int i = N-1;
45 
46         public boolean hasNext() {
47             return i >= 0;
48         }
49 
50         public Item next() {
51             if (!hasNext()) throw new NoSuchElementException();
52             return a[i--];
53         }
54 
55         public void remove() {
56             throw new UnsupportedOperationException();
57         }
58     }
59 
60 
61     public static void main(String[] args) {
62         int max = Integer.parseInt(args[0]);
63         FixedCapacityStack<String> stack = new FixedCapacityStack<String>(max);
64         while (!StdIn.isEmpty()) {
65             String item = StdIn.readString();
66             if (!item.equals("-")) stack.push(item); 
67             else if (stack.isEmpty())  StdOut.println("BAD INPUT"); 
68             else                       StdOut.print(stack.pop() + " ");
69         }
70         StdOut.println();
71 
72         // print what‘s left on the stack
73         StdOut.print("Left on stack: ");
74         for (String s : stack) {
75             StdOut.print(s + " ");
76         }
77         StdOut.println();
78     } 
79 } 

  1 package algorithms.ADT;
  2 
  3 /******************************************************************************
  4  *  Compilation:  javac ResizingArrayStack.java
  5  *  Execution:    java ResizingArrayStack < input.txt
  6  *  Dependencies: StdIn.java StdOut.java
  7  *  Data files:   http://algs4.cs.princeton.edu/13stacks/tobe.txt
  8  *  
  9  *  Stack implementation with a resizing array.
 10  *
 11  *  % more tobe.txt 
 12  *  to be or not to - be - - that - - - is
 13  *
 14  *  % java ResizingArrayStack < tobe.txt
 15  *  to be not that or be (2 left on stack)
 16  *
 17  ******************************************************************************/
 18 
 19 import java.util.Iterator;
 20 import java.util.NoSuchElementException;
 21 
 22 import algorithms.util.StdIn;
 23 import algorithms.util.StdOut;
 24 
 25 /**
 26  *  The <tt>ResizingArrayStack</tt> class represents a last-in-first-out (LIFO) stack
 27  *  of generic items.
 28  *  It supports the usual <em>push</em> and <em>pop</em> operations, along with methods
 29  *  for peeking at the top item, testing if the stack is empty, and iterating through
 30  *  the items in LIFO order.
 31  *  <p>
 32  *  This implementation uses a resizing array, which double the underlying array
 33  *  when it is full and halves the underlying array when it is one-quarter full.
 34  *  The <em>push</em> and <em>pop</em> operations take constant amortized time.
 35  *  The <em>size</em>, <em>peek</em>, and <em>is-empty</em> operations takes
 36  *  constant time in the worst case. 
 37  *  <p>
 38  *  For additional documentation,
 39  *  see <a href="http://algs4.cs.princeton.edu/13stacks">Section 1.3</a> of
 40  *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 41  *
 42  *  @author Robert Sedgewick
 43  *  @author Kevin Wayne
 44  */
 45 public class ResizingArrayStack<Item> implements Iterable<Item> {
 46     private Item[] a;         // array of items
 47     private int N;            // number of elements on stack
 48 
 49 
 50     /**
 51      * Initializes an empty stack.
 52      */
 53     public ResizingArrayStack() {
 54         a = (Item[]) new Object[2];
 55         N = 0;
 56     }
 57 
 58     /**
 59      * Is this stack empty?
 60      * @return true if this stack is empty; false otherwise
 61      */
 62     public boolean isEmpty() {
 63         return N == 0;
 64     }
 65 
 66     /**
 67      * Returns the number of items in the stack.
 68      * @return the number of items in the stack
 69      */
 70     public int size() {
 71         return N;
 72     }
 73 
 74 
 75     // resize the underlying array holding the elements
 76     private void resize(int capacity) {
 77         assert capacity >= N;
 78         Item[] temp = (Item[]) new Object[capacity];
 79         for (int i = 0; i < N; i++) {
 80             temp[i] = a[i];
 81         }
 82         a = temp;
 83     }
 84 
 85     /**
 86      * Adds the item to this stack.
 87      * @param item the item to add
 88      */
 89     public void push(Item item) {
 90         if (N == a.length) resize(2*a.length);    // double size of array if necessary
 91         a[N++] = item;                            // add item
 92     }
 93 
 94     /**
 95      * Removes and returns the item most recently added to this stack.
 96      * @return the item most recently added
 97      * @throws java.util.NoSuchElementException if this stack is empty
 98      */
 99     public Item pop() {
100         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
101         Item item = a[N-1];
102         a[N-1] = null;                              // to avoid loitering
103         N--;
104         // shrink size of array if necessary
105         if (N > 0 && N == a.length/4) resize(a.length/2);
106         return item;
107     }
108 
109 
110     /**
111      * Returns (but does not remove) the item most recently added to this stack.
112      * @return the item most recently added to this stack
113      * @throws java.util.NoSuchElementException if this stack is empty
114      */
115     public Item peek() {
116         if (isEmpty()) throw new NoSuchElementException("Stack underflow");
117         return a[N-1];
118     }
119 
120     /**
121      * Returns an iterator to this stack that iterates through the items in LIFO order.
122      * @return an iterator to this stack that iterates through the items in LIFO order.
123      */
124     public Iterator<Item> iterator() {
125         return new ReverseArrayIterator();
126     }
127 
128     // an iterator, doesn‘t implement remove() since it‘s optional
129     private class ReverseArrayIterator implements Iterator<Item> {
130         private int i;
131 
132         public ReverseArrayIterator() {
133             i = N-1;
134         }
135 
136         public boolean hasNext() {
137             return i >= 0;
138         }
139 
140         public void remove() {
141             throw new UnsupportedOperationException();
142         }
143 
144         public Item next() {
145             if (!hasNext()) throw new NoSuchElementException();
146             return a[i--];
147         }
148     }
149 
150 
151     /**
152      * Unit tests the <tt>Stack</tt> data type.
153      */
154     public static void main(String[] args) {
155         ResizingArrayStack<String> s = new ResizingArrayStack<String>();
156         while (!StdIn.isEmpty()) {
157             String item = StdIn.readString();
158             if (!item.equals("-")) s.push(item);
159             else if (!s.isEmpty()) StdOut.print(s.pop() + " ");
160         }
161         StdOut.println("(" + s.size() + " left on stack)");
162     }
163 }