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ReverseList.java
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package com.rrohit.algo.linkedlist;
public class ReverseList {
public Node reverseList(Node head) {
if (head == null) {
return null;
}
Node nextNode = null, prevNode = null, current= head;;
while (current != null) {
nextNode = current.getNext();
current.setNext(prevNode);
prevNode = current;
current = nextNode;
}
return prevNode;
}
public <T>Node<T> reverseListInPairs(Node<T> head){
if (head== null || head.getNext() == null) {
return head;
}
Node<T> current = head, temp =null, temp2 = null, prev = null;
head = head.getNext();
while (current!= null && current.getNext() != null) {
temp = current.getNext();
temp2 = temp.getNext();
temp.setNext(current);
current.setNext(temp2);
//prev will be used in 2nd pair onwards
if (prev != null) {
prev.setNext(temp);
}
prev = current;
current = current.getNext();
}
return head;
}
public <T>Node<T> reverseListInK(Node<T> head, int k){
Node<T> current = head,
prev = null,
nextNode = null;
int count =0;
while (current != null && count<k) {
nextNode = current.getNext();
current.setNext(prev);
prev = current;
current = nextNode;
count++;
}
if (nextNode != null) {
head.setNext(reverseListInK(nextNode, k));
}
return prev;
}
public static void main(String[] args) {
LinkedList<Integer> list = new LinkedList<Integer>();
for (int i=1; i<6; i++) {
list.add(i);
}
list.display();
ReverseList rl = new ReverseList();
/*Node head = rl.reverseList(list.getHead());
list.setHead(head);
list.display();*/
list.display();
/*Node head1 = rl.reverseListInPairs(list.getHead());
list.setHead(head1);
list.display();*/
Node head1 = rl.reverseListInK(list.getHead(),3);
list.setHead(head1);
list.display();
}
}