Add One to a Digit Chain

Medium

A non-negative integer is stored as a singly linked list digits: each node holds one digit, and the most significant digit is at the head. Add one to the number and return the head of a list that describes the result in the same form. If the number gets longer (as after 999), a new node must appear at the front.

Example 1

digits=list_node([4, 0, 7]) → [4, 0, 8]

407 + 1 = 408: only the last digit changes.

Example 2

digits=list_node([2, 9, 9]) → [3, 0, 0]

299 + 1 = 300: both nines turn into zeros and the carry bumps the 2.

Example 3

digits=list_node([9]) → [1, 0]

9 + 1 = 10: a new node appears at the front.

Constraints

1 ≤ number of nodes ≤ 100
0 ≤ Node.val ≤ 9
No leading zeros, except when the number itself is 0

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Topics

Linked List Math

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Input

digits=list_node([4, 0, 7])

Expected

[4, 0, 8]

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