206. Reverse Linked List

Question

LeetCode Problem

Image: View on LeetCode

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
  Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?

Solutions

ListNode* reverseList(ListNode* head) {
	ListNode* prev = nullptr;
	ListNode* curr = head;
	while (curr) {
		ListNode* next = curr->next;
		curr->next = prev;
		prev = curr;
		curr =next;
	}
	return prev;
}