1 package chap02;
2
3 import static org.junit.Assert.*;
4
5 import java.util.Arrays;
6
7 import org.junit.Test;
8
9 public class ques2_4 {
10 /**
11 * 逆序对，将一个序列中的所有逆序对打印输出
12 *
13 * @author xiaojintao
14 *
15 */
16 static void printReverseOrder(int[] n) {
17 int i = 0;
18 int j;
19 while (i < n.length - 1) {
20 for (j = i + 1; j < n.length; j++) {
21 if (n[i] > n[j]) {
22 System.out.println("<" + n[i] + "," + n[j] + ">");
23 }
24 }
25 i++;
26 }
27 }
28
29 @Test
30 public void testName() throws Exception {
31 int[] a = { 2 };
32 printReverseOrder(a);
33 }
34
35 /**
36 * 修改归并排序，使之打印出序列中的所有逆序对数
37 *
38 * @param n
39 */
40 static void printReverseByMergeSort(int[] n) {
41 int start = 0;
42 int end = n.length;
43 mergeSort(n, start, end);
44 ;
45 }
46
47 @Test
48 public void test() throws Exception {
49 int[] a = { 2, 3, 8, 6, 1, 5, 4, 0 };
50 printReverseByMergeSort(a);
51 }
52
53 /**
54 * 修改的归并排序算法用于逆序对输出
55 *
56 * @param a
57 * @return
58 */
59 protected static void mergeSort(int[] a, int start, int end) {
60 if (start < end - 1) {
61 int mid = (start + end) / 2;
62 mergeSort(a, start, mid);
63 mergeSort(a, mid, end);
64 merge(a, start, mid, end);
65 }
66 }
67
68 /**
69 * 输出逆序对
70 *
71 * @param a
72 * @param b
73 * @return
74 */
75 protected static void merge(int[] n, int start, int mid, int end) {
76 int[] l = Arrays.copyOfRange(n, start, mid);
77 int[] r = Arrays.copyOfRange(n, mid, end);
78 int i = 0;
79 int j = 0;// j<mid-start
80 int k = 0;// k<end-mid
81 while (i < end - start) {
82 if (j < mid - start & k < end - mid) {
83 if (l[j] < r[k]) {
84 n[i + start] = l[j];
85 j++;
86 } else {
87 System.out.println("<" + l[j] + "," + r[k] + ">");
88 n[i + start] = r[k];
89 k++;
90 }
91 } else if (k < end - mid) {
92 n[i + start] = r[k];
93 k++;
94 } else if (j < mid - start) {
95 n[i + start] = l[j];
96 j++;
97 }
98 i++;
99 }
100 }
101 }
