Description
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
1 | Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4) |
Solution
Can use Stack instead of List to store these two numbers1
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61/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
if (l1 == null && l2 == null) return l1;
if (l1 == null) return l2;
if (l2 == null) return l1;
List<Integer> num1 = new ArrayList<>();
List<Integer> num2 = new ArrayList<>();
while(l1 != null){
num1.add(l1.val);
l1 = l1.next;
}
while(l2 != null){
num2.add(l2.val);
l2 = l2.next;
}
int i = num1.size()-1;
int j = num2.size()-1;
int d = 0;
List<Integer> res = new ArrayList<>();
while(i >= 0 && j >= 0){
int tmp = num1.get(i) + num2.get(j) + d;
d = tmp /10;
res.add(tmp%10);
i--;
j--;
}
if (i >= 0){
for (int k = i; k >= 0; k--){
int tmp = num1.get(k) + d;
res.add(tmp%10);
d = tmp/10;
}
}
else if (j >= 0){
for (int k = j; k >= 0; k--){
int tmp = num2.get(k) + d;
res.add(tmp%10);
d = tmp/10;
}
}
if (d > 0) res.add(1);
ListNode head = new ListNode(0);
ListNode cur = head;
for (int k = res.size()-1; k >= 0; k--){
cur.next = new ListNode(res.get(k));
cur = cur.next;
}
return head.next;
}
}