README.md

206. Reverse Linked List

Given the head of a singly linked list, reverse the list, and return the reversed list.

Example 1

Input: head = [1,2,3,4,5]
Output: [5,4,3,2,1]

Example 2

Input: head = [1,2]
Output: [2,1]

Example 3

Input: head = []
Output: []

Constraints

• The number of nodes in the list is the range [0, 5000].
• -5000 <= Node.val <= 5000

📝 Note

There are 3 key variables we use to reverse a linked list:

1. head (global)
2. tail (global)
3. next (local)

head points to the given linked list that we want to reverse.

tail points to the reversed linked list, and this will be the answer.

next is used as a buffer to break the head of linked list and store the next node of it.

The steps are:

1. Use next to break the head of the linked list.
2. Point the tail to the head of tail
3. Re-point the head to next, which means re-defined the head of the linked list.
4. Iterate it until head is point to null (all list node has been visited)