88 * first, middle, and last elements in the list.
99 */
1010public class Exercise23_04 {
11- public static void main ( String [] args ) {
12- int [] list = { 2 , 3 , 2 , 5 , 6 , 1 , - 2 , 3 , 14 , 12 };
13- quickSort (list );
14- System . out . println ( "Sorted List: \n " + Arrays . toString ( list ) );
11+ public static void quickSort ( int [] list ) {
12+ /* Exercise 23.4 */
13+ int medianIdx = indexOfMedian (list );
14+ quickSort ( list , medianIdx , list . length - 1 );
1515 }
1616
1717 public static void quickSort (int [] list , int first , int last ) {
@@ -22,18 +22,12 @@ public static void quickSort(int[] list, int first, int last) {
2222 }
2323 }
2424
25- public static void quickSort (int [] list ) {
26- quickSort (list , 0 , list .length - 1 );
27- }
28- 2925 /**
3026 * Partition the array list[first..last]
3127 */
3228 public static int partition (int [] list , int first , int last ) {
33- /* Exercise 23_04 */
34- int pivotIdx = findMedian (list , first , last );
35- int pivot = list [pivotIdx ];
36- int low = first ; // Index for forward search
29+ int pivot = list [first ]; // Choose the first element as the pivot
30+ int low = first + 1 ; // Index for forward search
3731 int high = last ; // Index for backward search
3832
3933 while (high > low ) {
@@ -58,33 +52,40 @@ public static int partition(int[] list, int first, int last) {
5852
5953 // Swap pivot with list[high]
6054 if (pivot > list [high ]) {
61- list [pivotIdx ] = list [high ];
55+ list [first ] = list [high ];
6256 list [high ] = pivot ;
6357 return high ;
6458 } else {
65- return pivotIdx ;
59+ return first ;
6660 }
6761 }
6862
6963 /**
70- * Exercise 23.04 solution
7164 *
72- * @param list current list
73- * @param first current left index
74- * @param last current right index
75- * @return index of the median between first, last, and mid index values
65+ * @param list int array to find median of first, middle and last nums
66+ * @return the index of the median value
7667 */
77- static int findMedian (int [] list , int first , int last ) {
78- int midIdx = (first + last ) / 2 ;
79- int firstVal = list [first ];
80- int lastVal = list [last ];
81- int midVal = list [midIdx ];
82- int max = Math .max (Math .max (firstVal , lastVal ), midVal );
83- int min = Math .min (Math .min (firstVal , lastVal ), midVal );
84- if (midVal != min && midVal != max ) return midIdx ;
85- else if (lastVal != min && lastVal != max ) return last ;
86- else return first ;
68+ static int indexOfMedian (int [] list ) {
69+ int [] temp = {list [0 ], list [list .length / 2 ], list [list .length - 1 ]};
70+ Arrays .sort (temp );
71+ if (list [0 ] == temp [1 ]) {
72+ return 0 ;
73+ }
74+ else if (list [list .length / 2 ] == temp [1 ]) {
75+ return list .length / 2 ;
76+ }
77+ 78+ return list .length - 1 ;
79+ }
8780
81+ /**
82+ * A test method
83+ */
84+ public static void main (String [] args ) {
85+ int [] list = {2 , 3 , 2 , 5 , 6 , 1 , -2 , 3 , 14 , 12 };
86+ quickSort (list );
87+ for (int i = 0 ; i < list .length ; i ++)
88+ System .out .print (list [i ] + " " );
8889 }
8990}
9091
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