PROBLEM DESCRIPTION
Given a linked list, the task is to reverse every k node (where k is an input to the function) in the linked list. If the number of nodes is not a multiple of k then left-out nodes, in the end, should be considered as a group and must be reversed (See Example 2 for clarification).
SOLUTION
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class Solution {
public static Node reverse(Node node, int k) {
if(node == null)
return null;
int count = 0;
Node p1 = node;
for(int i=0; i<k-1; i++){
if(p1 == null)
break;
count++;
p1 = p1.next;
}
// last set of nodes
if(p1 == null)
return reverseLinkedList(node);
Node p2 = p1.next;
p1.next = null;
Node newHead = reverseLinkedList(node);
node.next = reverse(p2, k);
return newHead;
}
public static Node reverseLinkedList(Node head){
Node h1 = head;
Node h2 = null;
while(h1 != null){
Node t = h1;
h1 = h1.next;
t.next = h2;
h2 = t;
}
return h2;
}
}