2 Add Two Numbers
1. Question
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
Input:(2 -> 4 -> 3) + (5 -> 6 -> 4)
Output:7 -> 0 -> 8
Explanation: 342 + 465 = 807.
2. Implementation
/**
* 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) {
ListNode p1 = l1, p2 = l2;
ListNode dummy = new ListNode(0);
ListNode curNode = dummy;
int sum = 0;
while (p1 != null || p2 != null) {
if (p1 != null) {
sum += p1.val;
p1 = p1.next;
}
if (p2 != null) {
sum += p2.val;
p2 = p2.next;
}
curNode.next = new ListNode(sum % 10);
curNode = curNode.next;
sum /= 10;
}
if (sum != 0) {
curNode.next = new ListNode(sum);
}
return dummy.next;
}
}
3. Time & Space Complexity
时间复杂度O(m + n), m为第一个list的长度,n为第二个list的长度, 空间复杂度O(1)
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