369 Plus One Linked List

369. Plus One Linked List

1. Question

Given a non-negative integer represented asnon-emptya 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

2. Implementation

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode plusOne(ListNode head) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;

        ListNode lastNotNine = dummy, curNode = head;

        while (curNode != null) {
            if (curNode.val != 9) {
                lastNotNine = curNode;
            }
            curNode = curNode.next;
        }

        lastNotNine.val += 1;
        curNode = lastNotNine.next;

        while (curNode != null) {
            curNode.val = 0;
            curNode = curNode.next;
        }
        return dummy.val == 1 ? dummy : dummy.next;
    }
}

3. Time & Space Complexity

时间复杂度: O(n), 空间复杂度: O(1)