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Reverse a linked list

Tags : linkedlist, geeksforgeeks, cpp, easy

Problem Statement - link #

Given a linked list of N nodes. The task is to reverse this list.

Your Task: The task is to complete the function reverseList() with head reference as the only argument and should return new head after reversing the list.

Expected Time Complexity: O(N) Expected Auxiliary Space: O(1)

Examples #

Example 1:

Input:
LinkedList: 1->2->3->4->5->6
Output: 6 5 4 3 2 1
Explanation: After reversing the list, 
elements are 6->5->4->3->2->1.

Example 2:

Input:
LinkedList: 2->7->8->9->10
Output: 10 9 8 7 2
Explanation: After reversing the list,
elements are 10->9->8->7->2.

Constraints #

Solutions #

class Solution{
    public:
    //Function to reverse a linked list.
    struct Node* reverseList(struct Node *head)
    {
        // code here
        if(head==NULL || head->next==NULL) return head;
        Node* prev = NULL, *curr = head, *next;
        while(curr!=NULL){
            next = curr->next;
            curr->next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
        // return head of reversed list
    }
};