369. Plus One Linked List

Problem:

Given a non-negative integer represented as non-empty a singly linked list of digits, plus one to the integer.

You may assume the integer do not contain any leading zero, except the number 0 itself.

The digits are stored such that the most significant digit is at the head of the list.

Example:

Input:
1->2->3

Output:
1->2->4

Solutions:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode plusOne(ListNode head) {
        ListNode fakeHead = new ListNode(0);
        fakeHead.next = head;
        carry(fakeHead);
        if (fakeHead.val != 0) {
            return fakeHead;
        }
        return fakeHead.next;
    }
    private int carry(ListNode node) {
        if (node == null) {
            return 1;
        }
        int next = carry(node.next);
        if (next == 0) {
            return 0;
        }
        int tmp = node.val + next;
        node.val = tmp % 10;
        return tmp / 10;
    }
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode plusOne(ListNode head) {
        ListNode cur = head, right = null;
        while (cur != null) {
            if (cur.val != 9) right = cur;
            cur = cur.next;
        }
        if (right == null) {
            right = new ListNode(0);
            right.next = head;
            head = right;
        }
        ++right.val;
        cur = right.next;
        while (cur != null) {
            cur.val = 0;
            cur = cur.next;
        }
        return head;   
    }
}