# Reverse Linked List Groups - Amazon Top Interview Questions

### Problem Statement :

```Given a singly linked list node, and an integer k, reverse every k contiguous group of nodes.

Constraints

n ≤ 100,000 where n is the number of nodes in node

Example 1

Input

node = [0, 1, 2, 3]
k = 2

Output

[1, 0, 3, 2]

Example 2

Input

node = [0, 1, 2, 3]
k = 3

Output

[2, 1, 0, 3]```

### Solution :

```                        ```Solution in C++ :

/**
* class LLNode {
*     public:
*         int val;
*         LLNode *next;
* };
*/
LLNode* solve(LLNode* head, int k) {
stack<LLNode*> st;
int count = k;
while (head && count) {
LLNode* tmp = head;
tmp->next = NULL;
st.push(tmp);
--count;
}
LLNode *tmp_head_node = st.top(), *it_node = st.top();
st.pop();
while (st.size()) {
it_node->next = st.top();
st.pop();
it_node = it_node->next;
}
it_node->next = solve(head, k);
}
}```
```

```                        ```Solution in Python :

# class LLNode:
#     def __init__(self, val, next=None):
#         self.val = val
#         self.next = next
class Solution:
def solve(self, head, k):
temp = None
prev = None
count = 0
while cur != None and count < k:
temp = cur.next
cur.next = prev
prev = cur
cur = temp
count += 1
if temp is not None:
head.next = self.solve(temp, k)
return prev```
```

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