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206. Reverse Linked List

Question Link: https://leetcode.com/problems/reverse-linked-list/description/

Java Code #

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null)
            return head;
        ListNode tail = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return tail;
    }
}

C Code #

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* reverseList(struct ListNode* head) {
    if (head == NULL || head->next == NULL)
        return head;
    struct ListNode* h2 = reverseList(head->next);
    head->next->next = head;
    head->next = NULL;
    return h2;
}