LeetCode - Add Two Numbers
Problem description
You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order 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.
Example:
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Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
Analysis
the first thought is to use a loop to iterate all nodes of two pointer, which is the standard solution
Here’s the code:
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public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
ListNode dummy = new ListNode(0);
ListNode p = dummy;
int pre = 0;
while (l1 != null || l2 != null) {
int v1 = l1 == null ? 0 : l1.val;
int v2 = l2 == null ? 0 : l2.val;
int sum = v1 + v2 + pre;
pre = sum / 10;
ListNode next = new ListNode(sum % 10);
p.next = next;
p = p.next;
if (l1 != null){
l1 = l1.next;
}
if (l2 != null){
l2 = l2.next;
}
}
// missing this part get 1 WA
if (pre != 0){
p.next = new ListNode(1);
}
return dummy.next;
}
What to improve
- forget to deal with the edge case(the last pre = 1), need to think more carefully before submission