reverse-linked-list.md

Code

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */

func reverseList(head *ListNode) *ListNode {
	curr := head
	var prev *ListNode = nil
	var next *ListNode = nil

	for curr != nil {
		next = curr.Next
		curr.Next = prev
		prev = curr
		curr = next
	}

	head = prev

	return head
}

Solution in mind

• Keep track of 3 pointer, prev, curr and next. With curr being initialised to head and the others being nil.

• Move through curr till we reach the end of linked list.

• Set next as curr.Next. Now the current node's pointer can be set to the previous node.

• After updating the current node's pointer, move curr to next and prev to curr.

• Finally, set the new head as prev, this will update the head to the new beginning of the list.