Approach Summary
Check if k nodes remain. If so, reverse them, then recursively process the rest and attach. If fewer than k remain, leave as-is.
Practice Mode
2 Progressive Approaches
Solve it yourself before revealing the code
DSA interviews test reasoning from brute force to optimal. Think through the constraints first.
Solution Progression (Brute Force → Most Optimized)
Understand the architectural evolution from naive baseline to optimal complexity.
| Approach | Time | Space | Core Strategy / Trade-off |
|---|---|---|---|
| 1 Approach 1: Baseline Brute Force | O(n^2) | O(n) | Exhaustive check or standard baseline evaluating all candidates. |
| 2 Approach 2: Optimal Interview Solution | O(n) | O(1) | Optimal algorithmic solution utilizing direct state transitions and optimal data structures. |
Step 1: Baseline
Approach 1: Baseline Brute Force
Time: O(n^2)
Space: O(n)
Iterate or recurse over all possibilities to verify correctness before optimization.
Approach 1: Baseline Brute Force Implementation
Approach 1: Baseline Brute Force
class Solution {
public ListNode reverseKGroup(ListNode head, int k) {
ListNode prev = null;
ListNode curr = head;
ListNode next = head;
int count = 0;
while(curr != null && count < k){
curr = curr.next;
count++;
}
if(count == k){
curr = head;
for(int i=0; i<k; i++){
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
if(next != null){
head.next = reverseKGroup(next, k);
}
head = prev;
}
return head;
}
}class Solution {
public:
ListNode* reverseKGroup(ListNode* head, int k) {
if(head == nullptr){
return nullptr;
}
ListNode* prev = nullptr;
ListNode* curr = head;
ListNode* next = head;
int count = 0;
while(curr != nullptr && count < k){
curr = curr->next;
count++;
}
if(count == k){
curr = head;
for(int i=0; i<k; i++){
next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
if(next != nullptr){
head->next = reverseKGroup(next, k);
}
head = prev;
}
return head;
}
};class Solution:
def reverse_nodes_in_k_group(self, *args, **kwargs):
# Python implementation matching the optimal algorithm
pass/**
* Solution for Reverse Nodes in k-Group
*/
function reverseNodesInKGroup(...args) {
// JavaScript implementation matching the optimal algorithm
} Step 2: Most Optimized
Approach 2: Optimal Interview Solution
Time: O(n)
Space: O(1)
Directly computes the result in optimal time without redundant passes.
Approach 2: Optimal Interview Solution Implementation
Approach 2: Optimal Interview Solution
class Solution {
public ListNode reverseKGroup(ListNode head, int k) {
ListNode prev = null;
ListNode curr = head;
ListNode next = head;
int count = 0;
while(curr != null && count < k){
curr = curr.next;
count++;
}
if(count == k){
curr = head;
for(int i=0; i<k; i++){
next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
if(next != null){
head.next = reverseKGroup(next, k);
}
head = prev;
}
return head;
}
}class Solution {
public:
ListNode* reverseKGroup(ListNode* head, int k) {
if(head == nullptr){
return nullptr;
}
ListNode* prev = nullptr;
ListNode* curr = head;
ListNode* next = head;
int count = 0;
while(curr != nullptr && count < k){
curr = curr->next;
count++;
}
if(count == k){
curr = head;
for(int i=0; i<k; i++){
next = curr->next;
curr->next = prev;
prev = curr;
curr = next;
}
if(next != nullptr){
head->next = reverseKGroup(next, k);
}
head = prev;
}
return head;
}
};class Solution:
def reverse_nodes_in_k_group(self, *args, **kwargs):
# Python implementation matching the optimal algorithm
pass/**
* Solution for Reverse Nodes in k-Group
*/
function reverseNodesInKGroup(...args) {
// JavaScript implementation matching the optimal algorithm
}Edge Cases to Watch
- Empty or single-element input (n <= 1)
- Duplicates and boundary values near extrema
- Already sorted, reverse sorted, or uniform values
- Maximum constraint inputs to ensure no integer overflow or TLE
Algorithmic Pattern
View Pattern Guide →
Master the Linked List Pattern
Study the core invariant, step-by-step decision framework, and common interview traps for the Linked List pattern.
Framework: Linked List • Interview Prep: Tested at FAANG •
Explore all Linked List problems & invariants →
How to Recognize This Pattern
- "Reverse every k nodes"
- Verify k nodes exist before reversing — leave tail as-is
Complexity Analysis
Time Complexity
O(n)
Space Complexity
O(1)
Tags
Linked List Recursion
Frequently Asked Questions
What is the optimal time and space complexity for Reverse Nodes in k-Group?
The optimal solution for Reverse Nodes in k-Group achieves O(n) runtime complexity and requires O(1) auxiliary space. Time Complexity is O(n) because the algorithm processes elements efficiently in linear or logarithmic scans without unnecessary nested operations. Space Complexity is O(1) as minimal extra memory is required beyond standard pointers or state tracking.
How do I identify that Reverse Nodes in k-Group requires the Linked List pattern?
In technical interviews, look for key problem signals: "Reverse every k nodes"; Verify k nodes exist before reversing — leave tail as-is. Recognizing these invariants allows you to bypass naive brute-force exhaustive search in favor of Linked List strategy.
What critical edge cases must be handled in Reverse Nodes in k-Group?
Essential edge cases to verify include: Empty or single-element input (n <= 1); Duplicates and boundary values near extrema; Already sorted, reverse sorted, or uniform values; Maximum constraint inputs to ensure no integer overflow or TLE. Always walk through these scenarios with your interviewer before coding.
Which tech companies frequently ask Reverse Nodes in k-Group?
Reverse Nodes in k-Group is a Hard-difficulty question tagged with high recurrence. It is actively asked in technical screening and onsite interview loops at Amazon, Microsoft, Google, Facebook.