Chapter 2 algorithm basic questions 2-4 (Reverse Order)

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 * reverse order, print all reverse pairs in a sequence and output 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 (); 33} 34 35/** 36 * modify the merge order, print all reverse logarithm 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 (); 51} 52 53/** 54 * the modified Merge Sorting Algorithm is used to output 55*56 * @ param a 57 * @ return 58 */59 protected static void mergeSort (int [], 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 * output reverse order to 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}