2. Add Two Numbers
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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 contains a single digit. Add the two numbers and return the sum as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Example 1:
Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.
First accepted
Idea:
- Loop through lists
- add each value to the list
- reverse list
- calculate sum
- create linked list from reversed sum
class Solution:
def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
def createLinkedNode(values):
head = ListNode(values[0])
current = head
for i in values[1:]:
node = ListNode(i)
current.next = node
current = current.next
return head
res = None
vals_l1 = []
cur = l1
while cur:
vals_l1.append(cur.val)
cur = cur.next
vals_l2 = []
cur = l2
while cur:
vals_l2.append(cur.val)
cur = cur.next
s_l1 = ''
for i in reversed(vals_l1):
s_l1 += str(i)
s_l2 = ''
for i in reversed(vals_l2):
s_l2 += str(i)
ll_sum = int(s_l1) + int(s_l2)
values = []
for val in reversed(str(ll_sum)):
values.append(int(val))
res = createLinkedNode(values)
return res
Better solution
Idea:
Just like how you would sum two numbers on a piece of paper.
class Solution:
def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
dummyHead = ListNode(0)
curr = dummyHead
carry = 0
while l1 != None or l2 != None or carry != 0:
l1Val = l1.val if l1 else 0
l2Val = l2.val if l2 else 0
columnSum = l1Val + l2Val + carry
carry = columnSum // 10
newNode = ListNode(columnSum % 10)
curr.next = newNode
curr = newNode
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
return dummyHead.next
