Question Definition
You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself. Follow up: What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
Example:
Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 8 -> 0 -> 7
Java Solution
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
Stack<Integer> s1 = new Stack<Integer>();
Stack<Integer> s2 = new Stack<Integer>();
while(l1 != null) {
s1.push(l1.val);
l1 = l1.next;
};
while(l2 != null) {
s2.push(l2.val);
l2 = l2.next;
}
int sum = 0;
ListNode list = new ListNode(0);
while (!s1.empty() || !s2.empty()) {
if (!s1.empty()) sum += s1.pop();
if (!s2.empty()) sum += s2.pop();
list.val = sum % 10;
ListNode head = new ListNode(sum / 10);
head.next = list;
list = head;
sum /= 10;
}
return list.val == 0 ? list.next : list;
}
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