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2_AddTwoNumbers.py
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2_AddTwoNumbers.py
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# ----------------------------------
# Question 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:
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
'''
# ----------------------------------
# My Solution
# ----------------------------------
# Definition for singly-linked list.
class ListNode:
def __init__(self, x):
self.val = x
self.next = None
class Solution:
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
num1 = self.node2num(l1)
num2 = self.node2num(l2)
num = num1 + num2
return self.num2node(num)
def node2num(self, node):
if not node.next:
return node.val
return node.val + 10 * self.node2num(node.next)
def num2node(self, num):
node = ListNode(num % 10)
val = num // 10
if not val:
return node
node.next = self.num2node(val)
return node
# ----------------------------------
# Instruction
# ----------------------------------
class Solution:
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
dummy = ListNode(0)
current, carry = dummy, 0
while l1 or l2:
val = carry
if l1:
val += l1.val
l1 = l1.next
if l2:
val += l2.val
l2 = l2.next
carry = val // 10
val = val % 10
current.next = ListNode(val)
current = current.next
# the sum of last two nodes > 10
if carry:
current.next = ListNode(1)
return dummy.next