链表表示的2个数相加

问题描述

You are given two 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.

Example:
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

分析

从左至右同步遍历2个链表，依次相加每一位的数字，注意处理进位的情况即可。

时间复杂度为 O(n).

代码

# Definition for singly-linked list.
class ListNode(object):
  def __init__(self, x):
    self.val = x
    self.next = None

class Solution:
  def addTwoNumbers(self, l1, l2, c = 0):
    # Fill this in.
    result = ListNode(0)
    p = result
    
    addToNextPos = 0

    while True:
        r = 0
        if l1:
            r += l1.val
            l1 = l1.next
        if l2:
            r += l2.val
            l2 = l2.next
        r += addToNextPos
        if r >= 10:
            p.val = r - 10
            addToNextPos = 1
        else:
            p.val = r
            addToNextPos = 0
        
        if l1 or l2:
            p.next = ListNode(0)
            p = p.next
        else:
            break
    
    return result

l1 = ListNode(2)
l1.next = ListNode(4)
l1.next.next = ListNode(3)

l2 = ListNode(5)
l2.next = ListNode(6)
l2.next.next = ListNode(4)

result = Solution().addTwoNumbers(l1, l2)
while result:
  print result.val,
  result = result.next
# 7 0 8