算法Sedgewick第四版-第1章基础-2.1Elementary Sortss-002插入排序法(Insertion sort)

  1 package algorithms.elementary21;
  2 
  3 /******************************************************************************
  4  *  Compilation:  javac Insertion.java
  5  *  Execution:    java Insertion < input.txt
  6  *  Dependencies: StdOut.java StdIn.java
  7  *  Data files:   http://algs4.cs.princeton.edu/21sort/tiny.txt
  8  *                http://algs4.cs.princeton.edu/21sort/words3.txt
  9  *  
 10  *  Sorts a sequence of strings from standard input using insertion sort.
 11  *
 12  *  % more tiny.txt
 13  *  S O R T E X A M P L E
 14  *
 15  *  % java Insertion < tiny.txt
 16  *  A E E L M O P R S T X                 [ one string per line ]
 17  *
 18  *  % more words3.txt
 19  *  bed bug dad yes zoo ... all bad yet
 20  *
 21  *  % java Insertion < words3.txt
 22  *  all bad bed bug dad ... yes yet zoo   [ one string per line ]
 23  *
 24  ******************************************************************************/
 25 
 26 import java.util.Comparator;
 27 
 28 import algorithms.util.StdIn;
 29 import algorithms.util.StdOut;
 30 
 31 /**
 32  *  The <tt>Insertion</tt> class provides static methods for sorting an
 33  *  array using insertion sort.
 34  *  <p>
 35  *  This implementation makes ~ 1/2 N^2 compares and exchanges in
 36  *  the worst case, so it is not suitable for sorting large arbitrary arrays.
 37  *  More precisely, the number of exchanges is exactly equal to the number
 38  *  of inversions. So, for example, it sorts a partially-sorted array
 39  *  in linear time.
 40  *  <p>
 41  *  The sorting algorithm is stable and uses O(1) extra memory.
 42  *  <p>
 43  *  See <a href="http://algs4.cs.princeton.edu/21elementary/InsertionPedantic.java.html">InsertionPedantic.java</a>
 44  *  for a version that eliminates the compiler warning.
 45  *  <p>
 46  *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/21elementary">Section 2.1</a> of
 47  *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 48  *
 49  *  @author Robert Sedgewick
 50  *  @author Kevin Wayne
 51  */
 52 public class Insertion {
 53 
 54     // This class should not be instantiated.
 55     private Insertion() { }
 56 
 57     /**
 58      * Rearranges the array in ascending order, using the natural order.
 59      * @param a the array to be sorted
 60      */
 61     public static void sort(Comparable[] a) {
 62         int N = a.length;
 63         for (int i = 0; i < N; i++) {
 64             for (int j = i; j > 0 && less(a[j], a[j-1]); j--) {
 65                 exch(a, j, j-1);
 66             }
 67             assert isSorted(a, 0, i);
 68         }
 69         assert isSorted(a);
 70     }
 71 
 72     /**
 73      * Rearranges the subarray a[lo..hi] in ascending order, using the natural order.
 74      * @param a the array to be sorted
 75      * @param lo left endpoint
 76      * @param hi right endpoint
 77      */
 78     public static void sort(Comparable[] a, int lo, int hi) {
 79         for (int i = lo; i <= hi; i++) {
 80             for (int j = i; j > lo && less(a[j], a[j-1]); j--) {
 81                 exch(a, j, j-1);
 82             }
 83         }
 84         assert isSorted(a, lo, hi);
 85     }
 86 
 87     /**
 88      * Rearranges the array in ascending order, using a comparator.
 89      * @param a the array
 90      * @param comparator the comparator specifying the order
 91      */
 92     public static void sort(Object[] a, Comparator comparator) {
 93         int N = a.length;
 94         for (int i = 0; i < N; i++) {
 95             for (int j = i; j > 0 && less(a[j], a[j-1], comparator); j--) {
 96                 exch(a, j, j-1);
 97             }
 98             assert isSorted(a, 0, i, comparator);
 99         }
100         assert isSorted(a, comparator);
101     }
102 
103     /**
104      * Rearranges the subarray a[lo..hi] in ascending order, using a comparator.
105      * @param a the array
106      * @param lo left endpoint
107      * @param hi right endpoint
108      * @param comparator the comparator specifying the order
109      */
110     public static void sort(Object[] a, int lo, int hi, Comparator comparator) {
111         for (int i = lo; i <= hi; i++) {
112             for (int j = i; j > lo && less(a[j], a[j-1], comparator); j--) {
113                 exch(a, j, j-1);
114             }
115         }
116         assert isSorted(a, lo, hi, comparator);
117     }
118 
119 
120     // return a permutation that gives the elements in a[] in ascending order
121     // do not change the original array a[]
122     /**
123      * Returns a permutation that gives the elements in the array in ascending order.
124      * @param a the array
125      * @return a permutation <tt>p[]</tt> such that <tt>a[p[0]]</tt>, <tt>a[p[1]]</tt>,
126      *    ..., <tt>a[p[N-1]]</tt> are in ascending order
127      */
128     public static int[] indexSort(Comparable[] a) {
129         int N = a.length;
130         int[] index = new int[N];
131         for (int i = 0; i < N; i++)
132             index[i] = i;
133 
134         for (int i = 0; i < N; i++)
135             for (int j = i; j > 0 && less(a[index[j]], a[index[j-1]]); j--)
136                 exch(index, j, j-1);
137 
138         return index;
139     }
140 
141    /***************************************************************************
142     *  Helper sorting functions.
143     ***************************************************************************/
144     
145     // is v < w ?
146     private static boolean less(Comparable v, Comparable w) {
147         return v.compareTo(w) < 0;
148     }
149 
150     // is v < w ?
151     private static boolean less(Object v, Object w, Comparator comparator) {
152         return comparator.compare(v, w) < 0;
153     }
154         
155     // exchange a[i] and a[j]
156     private static void exch(Object[] a, int i, int j) {
157         Object swap = a[i];
158         a[i] = a[j];
159         a[j] = swap;
160     }
161 
162     // exchange a[i] and a[j]  (for indirect sort)
163     private static void exch(int[] a, int i, int j) {
164         int swap = a[i];
165         a[i] = a[j];
166         a[j] = swap;
167     }
168 
169    /***************************************************************************
170     *  Check if array is sorted - useful for debugging.
171     ***************************************************************************/
172     private static boolean isSorted(Comparable[] a) {
173         return isSorted(a, 0, a.length - 1);
174     }
175 
176     // is the array sorted from a[lo] to a[hi]
177     private static boolean isSorted(Comparable[] a, int lo, int hi) {
178         for (int i = lo+1; i <= hi; i++)
179             if (less(a[i], a[i-1])) return false;
180         return true;
181     }
182 
183     private static boolean isSorted(Object[] a, Comparator comparator) {
184         return isSorted(a, 0, a.length - 1, comparator);
185     }
186 
187     // is the array sorted from a[lo] to a[hi]
188     private static boolean isSorted(Object[] a, int lo, int hi, Comparator comparator) {
189         for (int i = lo + 1; i <= hi; i++)
190             if (less(a[i], a[i-1], comparator)) return false;
191         return true;
192     }
193 
194    // print array to standard output
195     private static void show(Comparable[] a) {
196         for (int i = 0; i < a.length; i++) {
197             StdOut.println(a[i]);
198         }
199     }
200 
201     /**
202      * Reads in a sequence of strings from standard input; insertion sorts them;
203      * and prints them to standard output in ascending order.
204      */
205     public static void main(String[] args) {
206         String[] a = StdIn.readAllStrings();
207         Insertion.sort(a);
208         show(a);
209     }
210 }