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?


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

Example 1


node = [1, 2, 3, 4]


[4, 3, 2, 1]

Example 2


node = [0, 1]


[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:
  , pre, head = pre, head,
        return pre

        if not node or not
            return node
        head = self.solve( = node = None
        return head

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