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All leaked interview problems are collected from Internet.

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

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