<p>You are given two <strong>non-empty</strong> linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.</p> <p>You may assume the two numbers do not contain any leading zero, except the number 0 itself.</p> <p> </p> <p><strong>Example 1:</strong></p> <img alt="" src="https://assets.leetcode.com/uploads/2021/04/09/sumii-linked-list.jpg" style="width: 523px; height: 342px;" /> <pre> <strong>Input:</strong> l1 = [7,2,4,3], l2 = [5,6,4] <strong>Output:</strong> [7,8,0,7] </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> l1 = [2,4,3], l2 = [5,6,4] <strong>Output:</strong> [8,0,7] </pre> <p><strong>Example 3:</strong></p> <pre> <strong>Input:</strong> l1 = [0], l2 = [0] <strong>Output:</strong> [0] </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li>The number of nodes in each linked list is in the range <code>[1, 100]</code>.</li> <li><code>0 <= Node.val <= 9</code></li> <li>It is guaranteed that the list represents a number that does not have leading zeros.</li> </ul> <p> </p> <p><strong>Follow up:</strong> Could you solve it without reversing the input lists?</p>