**Reverse a Linked List - Amazon Top Interview Questions**

### Problem Statement :

Given a singly linked list node, return its reverse. Bonus: Can you do this in \mathcal{O}(1)O(1) space? Constraints n ≤ 100,000 where n is the number of nodes in node Example 1 Input node = [1, 2, 3, 4] Output [4, 3, 2, 1] Example 2 Input node = [0, 1] Output [1, 0]

### Solution :

` ````
Solution in C++ :
/**
* class LLNode {
* public:
* int val;
* LLNode *next;
* };
*/
LLNode* solve(LLNode* node) {
if (node == NULL) return node;
LLNode *curr, *nextt;
curr = node;
if (node->next == NULL)
return node;
else {
nextt = curr->next;
curr->next = NULL;
while (nextt) {
LLNode* temp = nextt->next;
nextt->next = curr;
curr = nextt;
nextt = temp;
}
}
return curr;
}
```

` ````
Solution in Python :
class Solution:
def solve(self, node):
head, pre = node, None
while head:
head.next, pre, head = pre, head, head.next
return pre
"""
if not node or not node.next:
return node
head = self.solve(node.next)
node.next.next = node
node.next = None
return head
"""
```

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