Reverse a LinkedList

Problem statement: Reverse a LinkedList in java !

1. class Node5 {
2. Node5 next;
3. int data;
4. 
   
5. Node5(int data) {
6. this.data = data;
7. }
8. } // end of Node5
9. 
   
10. public class ReverseLinkedList {
11. 
    
12. Node5 head;
13. 
    
14. public static void main(String[] args) {
15. ReverseLinkedList l = new ReverseLinkedList();
16. l.add(3);
17. l.add(5);
18. l.add(8);
19. l.add(9);
20. l.print(l.head);
21. l.reverse();
22. System.out.println("\nafter reverse linked list");
23. l.print(l.head);
24. } // end of main()
25. 
    
26. // add the element in LinkedList
27. public void add(int data) {
28. Node5 next = new Node5(data);
29. if (head == null) {
30. head = next;
31. return;
32. }
33. Node5 last = head;
34. while (last.next != null) {
35. last = last.next;
36. }
37. last.next = next;
38. } // end of add()
39. 
    
40. // print the LinkedList
41. void print(Node5 next) {
42. Node5 temp = next;
43. while (temp != null) {
44. System.out.print(temp.data + "-->");
45. temp = temp.next;
46. }
47. } // end of print()
48. 
    
49. // reverse the LinkedList
50. Node5 reverse() {
51. Node5 prev = null;
52. Node5 current = head;
53. Node5 next = null;
54. while (current != null) {
55. next = current.next;
56. current.next = prev;
57. prev = current;
58. current = next;
59. }
60. head = prev;
61. return head;
62. } // end of reverse()
63. } //end of ReverseLinkedList 

Output: 

3-->5-->8-->9-->

after reverse linked list

9-->8-->5-->3-->

Reverse a string array !!

Problem statement: Reverse a string array in java !
Using for Loop:

1. public class ReverseStringArrayExe1 {
2. public static void main(String[] args) {
3. 
   
4. String a[] = { "apples", "tomatoes", "bananas", "guavas", "pineapples" };
5. for (int i = 0; i < a.length / 2; i++) {
6. Object temp = a[i];
7. a[i] = a[a.length - 1 - i];
8. a[a.length - 1 - i] = (String) temp;
9. 
   
10. }
11. for (String s : a) {
12. System.out.print(s + " ");
13. 
    
14. }
15. }
16. }

Output: 
pineapples guavas bananas tomatoes apples
Time complexity: O(n/2)

Using while Loop:

1. public class ReverseStringArray {
2. public static void main(String[] args) {
3. String a[] = { "apples", "tomatoes", "bananas", "guavas", "pineapples" };
4. int end = a.length - 1;
5. int start = 0;
6. String temp;
7. while (start < end) {
8. temp = a[start];
9. a[start] = a[end];
10. a[end] = temp;
11. start++;
12. end--;
13. }
14. for (String i : a) {
15. System.out.print(i + " ");
16. }
17. }
18. }

Output:

pineapples guavas bananas tomatoes apples

Time complexity: O(n/2)

Using Java 8 Stream API:

1. import java.util.stream.IntStream;
2. 
   
3. public class ReverseArrayUsingStream {
4. public static void main(String[] args) {
5. String a[] = { "apples", "tomatoes", "bananas", "guavas", "pineapples" };
6. reverseUsingStream(a);
7. }
8. 
   
9. static void reverseUsingStream(Object a[]) {
10. 
    
11. Object rev[] =IntStream.rangeClosed(1, a.length).mapToObj(i -> a[a.length - i]).toArray();
12. for (Object s : rev) {
13. System.out.print(s + " ");
14. }
15. }
16. }

Output:

pineapples guavas bananas tomatoes apples 

Using Collections.reverse() :

1. import java.util.List;
2. import java.util.Arrays;
3. import java.util.Collections;
4. 
   
5. public class ReverseArrayCollections {
6. public static void main(String[] args) {
7. String a[] = { "apples", "tomatoes", "bananas", "guavas", "pineapples" };
8. reverseUsingCollectionsUtils(a);
9. }
10. static void reverseUsingCollectionsUtils(Object[] array) {
11. List<Object> list = Arrays.asList(array);
12. Collections.reverse(list);
13. for (Object i : list) {
14. System.out.print(i + " ");
15. }
16. }
17. }

Output:

pineapples guavas bananas tomatoes apples

Reverse an integer array !!

Problem statement:  Reverse an integer array in java !
Using  for Loop:

1. public class ReverseNumberArray {
2. public static void main(String[] args) {
3. int a[] = { 2, 4, 6, 7, 3, 56, 34 };
4. for (int i = 0; i < a.length / 2; i++) {
5. int temp = a[i];
6. a[i] = a[a.length - 1 - i];
7. a[a.length - 1 - i] = temp;
8. }
9. for (int i : a) {
10. System.out.print(i + " ");
11. }
12. }
13. }

Output: 

34 56 3 7 6 4 2 

Time complexity: O(n/2)

Using while Loop:

1. public class ReverseNumberArray {
2. 
   
3. public static void main(String[] args) {
4. int a[] = { 2, 4, 6, 7, 3, 56, 34 };
5. 
   
6. int end = a.length - 1;
7. int start = 0;
8. Object temp;
9. while (start < end) {
10. temp = a[start];
11. a[start] = a[end];
12. a[end] = (int) temp;
13. start++;
14. end--;
15. }
16. for (int i : a) {
17. System.out.print(i + " ");
18. }
19. }
20. }

Output: 

34 56 3 7 6 4 2 

Time complexity: O(n/2)

Using Java 8 Stream API:

1. import java.util.stream.IntStream;
2. 
   
3. public class ReverseArrayUsingStream {
4. public static void main(String[] args) {
5. Integer a[] = { 2, 4, 6, 7, 3, 56, 34 };
6. reverseUsingStream(a);
7. }
8. 
   
9. static void reverseUsingStream(Object a[]) {
10. 
    
11. Object rev[] = IntStream.rangeClosed(1, a.length).mapToObj(i -> a[a.length - i]).toArray();
12. for (Object s : rev) {
13. System.out.print(s + " ");
14. }
15. }
16. }

Using Collections.reverse():

1. import java.util.List;
2. import java.util.Arrays;
3. import java.util.Collections;
4. 
   
5. public class ReverseArrayCollections {
6. public static void main(String[] args) {
7. 
   
8. Object a[] = { 2, 4, 6, 7, 3, 56, 34 };
9. reverseUsingCollectionsUtils(a);
10. }
11. static void reverseUsingCollectionsUtils(Object[] array) {
12. List<Object> list = Arrays.asList(array);
13. Collections.reverse(list);
14. for (Object i : list) {
15. System.out.print(i + " ");
16. }
17. }
18. }

Output:
34 56 3 7 6 4 2