L369. Plus One Linked List

LinkedList

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]

Solution:

• two pointers, which are adjacent.

• j will reach at the last index and check it is 9 or not;

public ListNode plusOne(ListNode head){
    ListNode dummy = new ListNode(0);
    dummy.next = head;
    ListNode i = dummy, j = dummy;
    
    while(j.next != null){
        j = j.next;
        if(j.val != 9) i = j;
    }
    if(j.val != 9){
        j.val++;
    }else{
        i.val++;
        i = i.next;
        while(i != null){
            i.val = 0;
            i = i.next;
        }
    }
    if(dummy.val == 0) return dummy.next;
    return dummy;
}