g0001_0100.s0025_reverse_nodes_in_k_group.Solution Maven / Gradle / Ivy
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Java-based LeetCode algorithm problem solutions, regularly updated
package g0001_0100.s0025_reverse_nodes_in_k_group;
// #Hard #Top_100_Liked_Questions #Linked_List #Recursion #Data_Structure_II_Day_13_Linked_List
// #Udemy_Linked_List #2023_08_09_Time_0_ms_(100.00%)_Space_43_MB_(88.08%)
import com_github_leetcode.ListNode;
/*
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
public class Solution {
public ListNode reverseKGroup(ListNode head, int k) {
if (head == null || head.next == null || k == 1) {
return head;
}
int j = 0;
ListNode len = head;
// loop for checking the length of the linklist, if the linklist is less than k, then return
// as it is.
while (j < k) {
if (len == null) {
return head;
}
len = len.next;
j++;
}
// Reverse linked list logic applied here.
ListNode c = head;
ListNode n = null;
ListNode prev = null;
int i = 0;
// Traverse the while loop for K times to reverse the node in K groups.
while (i != k) {
n = c.next;
c.next = prev;
prev = c;
c = n;
i++;
}
// C1 is pointing to 1st node of K group, which is now going to point to the next K group
// linklist.
// recursion, for futher remaining linked list.
head.next = reverseKGroup(n, k);
return prev;
}
}