1 /*
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3  *
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5  * modification, are permitted provided that the following conditions
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9  *     notice, this list of conditions and the following disclaimer.
10  *
11  *   - Redistributions in binary form must reproduce the above copyright
12  *     notice, this list of conditions and the following disclaimer in the
13  *     documentation and/or other materials provided with the distribution.
14  *
15  *   - Neither the name of Oracle nor the names of its
16  *     contributors may be used to endorse or promote products derived
17  *     from this software without specific prior written permission.
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19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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30  */
31 
32 /*
33  * This source code is provided to illustrate the usage of a given feature
34  * or technique and has been deliberately simplified. Additional steps
35  * required for a production-quality application, such as security checks,
36  * input validation and proper error handling, might not be present in
37  * this sample code.
38  */
39 
40 
41 
42 /**
43  * A quick sort demonstration algorithm
44  * SortAlgorithm.java
45  *
46  * @author James Gosling
47  * @author Kevin A. Smith
48  */
49 public class QSortAlgorithm extends SortAlgorithm {
50 
51     /**
52      * A version of pause() that makes it easier to ensure that we pause
53      * exactly the right number of times.
54      */
pauseTrue(int lo, int hi)55     private boolean pauseTrue(int lo, int hi) throws Exception {
56         super.pause(lo, hi);
57         return true;
58     }
59 
60     /** This is a generic version of C.A.R Hoare's Quick Sort
61      * algorithm.  This will handle arrays that are already
62      * sorted, and arrays with duplicate keys.<BR>
63      *
64      * If you think of a one dimensional array as going from
65      * the lowest index on the left to the highest index on the right
66      * then the parameters to this function are lowest index or
67      * left and highest index or right.  The first time you call
68      * this function it will be with the parameters 0, a.length - 1.
69      *
70      * @param a       an integer array
71      * @param lo0     left boundary of array partition
72      * @param hi0     right boundary of array partition
73      */
QuickSort(int a[], int lo0, int hi0)74     void QuickSort(int a[], int lo0, int hi0) throws Exception {
75         int lo = lo0;
76         int hi = hi0;
77         int mid;
78 
79         if (hi0 > lo0) {
80 
81             /* Arbitrarily establishing partition element as the midpoint of
82              * the array.
83              */
84             mid = a[(lo0 + hi0) / 2];
85 
86             // loop through the array until indices cross
87             while (lo <= hi) {
88                 /* find the first element that is greater than or equal to
89                  * the partition element starting from the left Index.
90                  */
91                 while ((lo < hi0) && pauseTrue(lo0, hi0) && (a[lo] < mid)) {
92                     ++lo;
93                 }
94 
95                 /* find an element that is smaller than or equal to
96                  * the partition element starting from the right Index.
97                  */
98                 while ((hi > lo0) && pauseTrue(lo0, hi0) && (a[hi] > mid)) {
99                     --hi;
100                 }
101 
102                 // if the indexes have not crossed, swap
103                 if (lo <= hi) {
104                     swap(a, lo, hi);
105                     ++lo;
106                     --hi;
107                 }
108             }
109 
110             /* If the right index has not reached the left side of array
111              * must now sort the left partition.
112              */
113             if (lo0 < hi) {
114                 QuickSort(a, lo0, hi);
115             }
116 
117             /* If the left index has not reached the right side of array
118              * must now sort the right partition.
119              */
120             if (lo < hi0) {
121                 QuickSort(a, lo, hi0);
122             }
123 
124         }
125     }
126 
swap(int a[], int i, int j)127     private void swap(int a[], int i, int j) {
128         int T;
129         T = a[i];
130         a[i] = a[j];
131         a[j] = T;
132 
133     }
134 
135     @Override
sort(int a[])136     public void sort(int a[]) throws Exception {
137         QuickSort(a, 0, a.length - 1);
138     }
139 }
140