LeetCode 445 - Add Two Numbers II (Medium)

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

 

 方法：按照题意做就可以

time complexity: O(n) space complexity: O(n)

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        s1 = self.getNumberString(l1)
        s2 = self.getNumberString(l2)
        
        num = str(int(s1) + int(s2))
        
        dummy = ListNode(0)
        cur = ListNode(int(num[0]))
        dummy.next = cur 
        
        for i in range(1, len(num)):
            _next = ListNode(int(num[i]))
            cur.next = _next 
            cur = cur.next
 
        return dummy.next
    
    def getNumberString(self, l):
        res = ""
        
        cur = l 
        while cur:
            res += str(cur.val)
            cur = cur.next 
            
        return res