2. Add Two Numbers - Medium
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.
用一个dummy node记录相加后的结果,同时还需要一个node记录dummy linked list的头,用以最后return
在循环里,用sum和remainder分别表示两位的加和、进位值。注意最后如果进位值不为0,还需要增加一个新的listnode
注意dummy linked list的处理:dummy.next = new listnode(xxx), dummy = dummy.next
time: O(n), space: O(n)
/** * 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) { int remainder = 0; ListNode dummy = new ListNode(0); ListNode prehead = dummy; while(l1 != null || l2 != null) { int sum = remainder; if(l1 != null) { sum += l1.val; l1 = l1.next; } if(l2 != null) { sum += l2.val; l2 = l2.next; } ListNode tmp = new ListNode(sum % 10); remainder = sum / 10; dummy.next = tmp; dummy = dummy.next; } if(remainder != 0) { dummy.next = new ListNode(remainder); } return prehead.next; } }
二刷:
class Solution { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { ListNode dummy = new ListNode(0); ListNode cur = dummy; int carry = 0; while(l1 != null || l2 != null) { if(l1 != null) { carry += l1.val; l1 = l1.next; } if(l2 != null) { carry += l2.val; l2 = l2.next; } cur.next = new ListNode(carry % 10); cur = cur.next; carry /= 10; } if(carry != 0) { cur.next = new ListNode(carry); } return dummy.next; } }